1.
Iron
–
Iron is a chemical element with symbol Fe and atomic number 26. It is a metal in the first transition series and it is by mass the most common element on Earth, forming much of Earths outer and inner core. It is the fourth most common element in the Earths crust, like the other group 8 elements, ruthenium and osmium, iron exists in a wide range of oxidation states, −2 to +6, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen, fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust. Unlike the metals that form passivating oxide layers, iron oxides occupy more volume than the metal and thus flake off, Iron metal has been used since ancient times, although copper alloys, which have lower melting temperatures, were used even earlier in human history. Pure iron is soft, but is unobtainable by smelting because it is significantly hardened and strengthened by impurities, in particular carbon. A certain proportion of carbon steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to pig iron, further refinement with oxygen reduces the carbon content to the correct proportion to make steel. Steels and iron alloys formed with metals are by far the most common industrial metals because they have a great range of desirable properties. Iron chemical compounds have many uses, Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. Iron forms binary compounds with the halogens and the chalcogens, among its organometallic compounds is ferrocene, the first sandwich compound discovered. Iron plays an important role in biology, forming complexes with oxygen in hemoglobin and myoglobin. Iron is also the metal at the site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants. A human male of average height has about 4 grams of iron in his body and this iron is distributed throughout the body in hemoglobin, tissues, muscles, bone marrow, blood proteins, enzymes, ferritin, hemosiderin, and transport in plasma. The mechanical properties of iron and its alloys can be evaluated using a variety of tests, including the Brinell test, Rockwell test, the data on iron is so consistent that it is often used to calibrate measurements or to compare tests. An increase in the content will cause a significant increase in the hardness. Maximum hardness of 65 Rc is achieved with a 0. 6% carbon content, because of the softness of iron, it is much easier to work with than its heavier congeners ruthenium and osmium. Because of its significance for planetary cores, the properties of iron at high pressures and temperatures have also been studied extensively
Iron
–
Iron, 26 Fe
Iron
–
Spectral lines of iron
Iron
–
Iron meteorites, similar in composition to the Earth's inner- and outer core
Iron
–
Hydrated
iron(III) chloride, also known as ferric chloride
2.
Banded iron formation
–
Banded iron formations are distinctive units of sedimentary rock that are almost always of Precambrian age. Some of the oldest known rock formations, formed over 3,700 million years ago, Banded layers rich in iron were mostly deposited between 2,400 and 1,900 mya. Phanerozoic ironstones generally have a different genesis, Banded iron beds are an important commercial source of iron ore, such as the Pilbara region of Western Australia and the Animikie Group in Minnesota. The formations are abundant around the time of the great event,2,400 million years ago. The conventional concept is that the banded iron layers were formed in sea water as the result of oxygen released by photosynthetic cyanobacteria. The oxygen then combined with dissolved iron in Earths oceans to form insoluble iron oxides, which precipitated out, forming a layer on the ocean floor. Each band is similar to a varve, to the extent that the banding is assumed to result from variations in available oxygen. It is unclear whether these banded ironstone formations were seasonal, followed some feedback oscillation in the complex system or followed some other cycle. It is assumed that initially the Earth started with vast amounts of iron, as photosynthetic organisms generated oxygen, the available iron in the Earths oceans precipitated out as iron oxides. An alternative explanation of these deposits has undergone much discussion as part of the Snowball Earth hypothesis. Several hypotheses exist for the initiation of the Snowball Earths, in a Snowball Earth state the earths continents, and possibly seas at low latitudes, were subject to an ice age. If this was the case, Earths free oxygen may have nearly or totally depleted during a severe ice age circa 750 to 580 million years ago. Dissolved iron then accumulated in the oxygen-poor oceans, following the thawing of the Earth, the seas became oxygenated once more causing the precipitation of the iron. Another mechanism for BIFs, also proposed in the context of the Snowball Earth discussion, is by deposition from metal-rich brines in the vicinity of hydrothermally active rift zones, alternatively, some geochemists suggest that BIFs could form by direct oxidation of iron by microbial anoxygenic phototrophs. Northern Minnesotas banded iron formations lie directly underneath a layer of material only recently recognized as ejecta from the Sudbury Basin impact. At the time of formation Earth had a single supercontinent called Columbia with substantial continental shelves, an asteroid slammed into waters about 1,000 m deep some 1.85 billion years ago. Computer models suggest that the tsunami would have been at least 1,000 m at the epicentre and those immense waves and large underwater landslides triggered by the impact stirred the ocean, bringing oxygenated waters from the surface down to the ocean floor. Sediments deposited on the seafloor before the impact, including BIFs contained little if any oxidized iron and this Fe to Fe ratio suggests that most parts of the ocean were relatively devoid of oxygen
Banded iron formation
–
Banded iron formation,
Karijini National Park,
Western Australia
Banded iron formation
–
2.1 billion year old rock showing banded iron formation
Banded iron formation
–
Close-up of banded iron formation specimen from Upper Michigan. Scale bar is 5.0 mm.
Banded iron formation
–
An ashtray carved out of a soft form of banded ironstone from the 3.5 billion year old
Barbeton Supergroup in South Africa. The red layers were laid down during the daylight hours when Archaean photosynthesizing cyanobacteria produced oxygen that immediately reacted with dissolved iron compounds in the water, to form insoluble iron oxide (rust). The white layers are sediments that settled during the night when there was no oxygen in the water.
3.
Manganese
–
Manganese is a chemical element with symbol Mn and atomic number 25. It is not found as an element in nature, it is often found in minerals in combination with iron. Manganese is a metal with important industrial metal alloy uses, particularly in stainless steels, by the mid-18th century, Swedish chemist Carl Wilhelm Scheele had used pyrolusite to produce chlorine. Scheele and others were aware that pyrolusite contained a new element, johan Gottlieb Gahn was the first to isolate an impure sample of manganese metal in 1774, which he did by reducing the dioxide with carbon. Manganese phosphating is used for rust and corrosion prevention on steel, ionized manganese is used industrially as pigments of various colors, which depend on the oxidation state of the ions. The permanganates of alkali and alkaline earth metals are powerful oxidizers, Manganese dioxide is used as the cathode material in zinc-carbon and alkaline batteries. In biology, manganese ions function as cofactors for a variety of enzymes with many functions. Manganese enzymes are essential in detoxification of superoxide free radicals in organisms that must deal with elemental oxygen. Manganese also functions in the complex of photosynthetic plants. The element is a trace mineral for all known living organisms but is a neurotoxin. In larger amounts, and apparently with far greater effectiveness through inhalation, Manganese is a silvery-gray metal that resembles iron. It is hard and very brittle, difficult to fuse, Manganese metal and its common ions are paramagnetic. Manganese tarnishes slowly in air and oxidizes like iron in water containing dissolved oxygen, naturally occurring manganese is composed of one stable isotope, 55Mn. Eighteen radioisotopes have been isolated and described, the most stable being 53Mn with a half-life of 3.7 million years, 54Mn with a half-life of 312.3 days, and 52Mn with a half-life of 5.591 days. All of the radioactive isotopes have half-lives of less than three hours, and the majority of less than one minute. Manganese also has three meta states, Manganese is part of the iron group of elements, which are thought to be synthesized in large stars shortly before the supernova explosion. 53Mn decays to 53Cr with a half-life of 3.7 million years, because of its relatively short half-life, 53Mn is relatively rare, produced by cosmic rays impact on iron. Manganese isotopic contents are combined with chromium isotopic contents and have found application in isotope geology
Manganese
–
Manganese, 25 Mn
Manganese
–
Electrolytically refined manganese chips and 1 cm 3 cube
Manganese
–
Manganese(II) chloride crystals – the pale pink color of Mn(II) salts is due to a spin-forbidden 3d transition.
Manganese
–
Aqueous solution of KMnO 4 illustrating the deep purple of Mn(VII) as it occurs in permanganate
4.
Psilomelane
–
Psilomelane is a group name for hard black manganese oxides including hollandite and romanechite. Psilomelane consists of manganese oxide with variable amounts of barium and potassium. Psilomelane is erroneously, and uncommonly, known as hematite, despite not being related to true hematite. Generalized formula may be represented as Ba8O164 or as 2Mn5O10 and it is sometimes considered to be a hydrous manganese manganate, but of doubtful composition. The amount of manganese present corresponds to 70-80% of manganous oxide with 10-15% of available oxygen, Psilomelane is amorphous and occurs as botryoidal and stalactitic masses with a smooth shining surface and submetallic lustre. The mineral is readily distinguished from other hydrous manganese oxides by its greater hardness 5 to 6, the streak is brownish black and the fracture smooth. Owing to its amorphous nature, the mineral often contains admixed impurities and it is soluble in hydrochloric acid with evolution of chlorine gas. The name has reference to this appearance, from the Greek for and. It is a common and important ore of manganese, occurring under the same conditions, with pyrolusite it is extensively mined in Vermont, Virginia, Arkansas, and Nova Scotia. Other manganese oxides, Birnessite Pyrolusite This article incorporates text from a now in the public domain, Chisholm, Hugh. Mindat with locality data Webmineral Mineral galleries
Psilomelane
–
A native sample of psilomelane
Psilomelane
–
Dendritic psilomelane on a cobble
Psilomelane
–
Polished specimen of manganese ore from the
Batesville, Arkansas district. Slab of manganese ore showing an intimate mixture of
hausmannite and psilomelane in a roughly zonal arrangement and a radiating mass of white
barite at the center. The light steel-gray mineral and the black mineral immediately adjacent to the barite are psilomelane. The rest of the black mineral is hausmannite. Natural size.
5.
Lead
–
Lead is a chemical element with atomic number 82 and symbol Pb. When freshly cut, it is bluish-white, it tarnishes to a dull gray upon exposure to air and it is a soft, malleable, and heavy metal with a density exceeding that of most common materials. Lead has the second-highest atomic number of the stable elements. Lead is a relatively unreactive post-transition metal and its weak metallic character is illustrated by its amphoteric nature and tendency to form covalent bonds. Compounds of lead are found in the +2 oxidation state. Exceptions are mostly limited to organolead compounds, like the lighter members of the group, lead exhibits a tendency to bond to itself, it can form chains, rings, and polyhedral structures. Lead is easily extracted from its ores and was known to people in Western Asia. A principal ore of lead, galena, often bears silver, Lead production declined after the fall of Rome and did not reach comparable levels again until the Industrial Revolution. Nowadays, global production of lead is about ten million tonnes annually, Lead has several properties that make it useful, high density, low melting point, ductility, and relative inertness to oxidation. In the late 19th century, lead was recognized as poisonous, Lead is a neurotoxin that accumulates in soft tissues and bones, damaging the nervous system and causing brain disorders and, in mammals, blood disorders. A lead atom has 82 electrons, arranged in a configuration of 4f145d106s26p2. The combined first and second ionization energies—the total energy required to remove the two 6p electrons—is close to that of tin, leads upper neighbor in group 14. This is unusual since ionization energies generally fall going down a group as an elements outer electrons become more distant from the nucleus, the similarity is caused by the lanthanide contraction—the decrease in element radii from lanthanum to lutetium, and the relatively small radii of the elements after hafnium. The contraction is due to shielding of the nucleus by the lanthanide 4f electrons. The combined first four ionization energies of lead exceed those of tin, for this reason lead, unlike tin, mostly forms compounds in which it has an oxidation state of +2, rather than +4. Relativistic effects, which become particularly prominent at the bottom of the periodic table, as a result, the 6s electrons of lead become reluctant to participate in bonding, a phenomenon called the inert pair effect. A related outcome is that the distance between nearest atoms in crystalline lead is unusually long, the lighter group 14 elements form stable or metastable allotropes having the tetrahedrally coordinated and covalently bonded diamond cubic structure. The energy levels of their outer s- and p-orbitals are close enough to allow mixing into four hybrid sp3 orbitals
Lead
–
Lead, 82 Pb
Lead
–
A sample of freshly solidified lead (from molten state)
Lead
–
World lead production peaking in the
Roman period and the rising
Industrial Revolution
Lead
–
Lead
ingots from
Roman Britain on display at the
Wells and Mendip Museum
6.
Galena
–
Galena, also called lead glance, is the natural mineral form of lead sulfide. It is the most important ore of lead and an important source of silver, Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the crystal system often showing octahedral forms. It is often associated with the minerals sphalerite, calcite and fluorite, Galena is the main ore of lead, used since ancient times. Because of its low melting point, it was easy to liberate by smelting. In some deposits galena contains about 1–2% silver, a byproduct that far outweighs the main ore in revenue. Galena deposits often contain significant amounts of silver as included silver sulfide mineral phases or as limited solid solution within the galena structure. These argentiferous galenas have long been the most important ore of silver, Galena deposits are found worldwide in various environments. Galena also occurs in North African countries and at Mount Hermon in Northern Israel, in the United States, it occurs most notably in the Mississippi Valley type deposits of the Lead Belt in southeastern Missouri, and in the Driftless Area of Illinois, Iowa and Wisconsin. The economic importance of galena to the history of the Driftless Area was so great that one of the towns in the region was named Galena. Galena also was a mineral of the zinc-lead mines of the tri-state district around Joplin in southwestern Missouri. Galena is also an important ore mineral in the mining regions of Colorado, Idaho, Utah. Of the latter, the Coeur dAlene district of northern Idaho was most prominent, Galena is the official state mineral of the U. S. states of Missouri and Wisconsin, the former mining town of Galena, Kansas takes its name from deposits of this mineral. Derbyshire in the UK was one of the areas where galena was mined. The largest documented crystal of galena is composite cubo-octahedra from the Great Laxey Mine, Isle of Man, Galena belongs to the octahedral sulfide group of minerals that have metal ions in octahedral positions, such as the iron sulfide pyrrhotite and the nickel arsenide niccolite. The galena group is named after its most common member, with other members that include manganese bearing alabandite and niningerite. Divalent lead cations and sulfur anions form a cubic unit cell much like the mineral halite of the halide mineral group. Zinc, cadmium, iron, copper, antimony, arsenic, bismuth, selenium substitutes for sulfur in the structure constituting a solid solution series
Galena
–
Galena close-up
Galena
–
Galena with
baryte and
pyrite from
Cerro de Pasco,
Peru (5.8×4.8×4.4 cm)
Galena
–
Galena with
druzy calcite
Galena
–
Cubic galena with calcite from Jasper County, Missouri, USA (size: 5.1×3.2×2.8 cm)
7.
Anglesite
–
Anglesite is a lead sulfate mineral with the chemical formula PbSO4. It occurs as a product of primary lead sulfide ore. Anglesite occurs as prismatic crystals and earthy masses, and is isomorphous with barite. It contains 74% of lead by mass and therefore has a specific gravity of 6.3. Anglesites color is white or gray with yellow streaks. It may be dark gray if impure, crystals from some other localities, notably from Monteponi in Sardinia, are transparent and colourless, possessed of a brilliant adamantine lustre, and usually modified by numerous bright faces. There are distinct cleavages parallel to the faces of the prism and the basal plane, Anglesite is a mineral of secondary origin, having been formed by the oxidation of galena in the upper parts of mineral lodes where these have been affected by weathering processes. At Monteponi the crystals encrust cavities in glistening granular galena, and from Leadhills, in Scotland, pseudomorphs of anglesite after galena are known. At most localities it is found as isolated crystals in the lodes, but at some places, in Australia and Mexico, it occurs as large masses. Anglesite is sometimes used a gemstone, lead sulfate This article incorporates text from a publication now in the public domain, Chisholm, Hugh, ed. Anglesite
Anglesite
–
Anglesite Touizit Morroco
Anglesite
–
Anglesite crystal from Touissit District, Morocco (size: 2.8×1.6×0.5 cm)
Anglesite
–
Angeliste from Monteponi Mine, Iglesias, Carbonia-Iglesias Province (size:15.3x7cm)
8.
Gold
–
Gold is a chemical element with symbol Au and atomic number 79. In its purest form, it is a bright, slightly yellow, dense, soft, malleable. Chemically, gold is a metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions, Gold often occurs in free elemental form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. It occurs in a solid solution series with the element silver and also naturally alloyed with copper. Less commonly, it occurs in minerals as gold compounds, often with tellurium, golds atomic number of 79 makes it one of the higher numbered, naturally occurring elements. It is thought to have produced in supernova nucleosynthesis, from the collision of neutron stars. Because the Earth was molten when it was formed, almost all of the present in the early Earth probably sank into the planetary core. Gold is resistant to most acids, though it does dissolve in aqua regia, a mixture of acid and hydrochloric acid. Gold also dissolves in solutions of cyanide, which are used in mining and electroplating. Gold dissolves in mercury, forming amalgam alloys, but this is not a chemical reaction, as a precious metal, gold has been used for coinage, jewelry, and other arts throughout recorded history. A total of 186,700 tonnes of gold is in existence above ground, the world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry. Gold is also used in infrared shielding, colored-glass production, gold leafing, certain gold salts are still used as anti-inflammatories in medicine. As of 2014, the worlds largest gold producer by far was China with 450 tonnes, Gold is cognate with similar words in many Germanic languages, deriving via Proto-Germanic *gulþą from Proto-Indo-European *ǵʰelh₃-. The symbol Au is from the Latin, aurum, the Latin word for gold, the Proto-Indo-European ancestor of aurum was *h₂é-h₂us-o-, meaning glow. This word is derived from the root as *h₂éu̯sōs, the ancestor of the Latin word Aurora. This etymological relationship is presumably behind the frequent claim in scientific publications that aurum meant shining dawn, Gold is the most malleable of all metals, a single gram can be beaten into a sheet of 1 square meter, and an avoirdupois ounce into 300 square feet. Gold leaf can be thin enough to become semi-transparent
Gold
–
Gold, 79 Au
Gold
–
Moche gold necklace depicting feline heads.
Larco Museum Collection. Lima-Peru
Gold
–
Mirror for the future
James Webb Space Telescope coated in gold to reflect infrared light
Gold
–
The
world's largest gold bar has a mass of 250 kg.
Toi museum,
Japan.
9.
Pachuca
–
Pachuca, formally known as Pachuca de Soto, is the capital and largest city of the Mexican state of Hidalgo. It is located in the part of the state. Pachuca de Soto is also the name of the municipality of which the city serves as municipal seat, Pachuca is located about 90 kilometres from Mexico City via Mexican Federal Highway 85. There is no consensus about the origin of the name Pachuca and it has been traced to the word pachoa, Pachoacan, and patlachuican. The official name of Pachuca is Pachuca de Soto in honor of congressman Manuel Fernando Soto and its nickname of “La bella airosa” comes from the strong winds that blow into the valley through the canyons to the north of the city. In the indigenous Otomi language, Pachuca is known as Nju̱nthe, the area had been long inhabited, but except for some green obsidian the mining that Pachuca is famous for began in the mid-16th century, during Spanish colonial rule. Pachuca remained a major mining center until the mid-20th century, with the city’s fortunes going up, in the mid-20th century a major downturn in mining pushed Pachuca to change the basis of its economy to industry, resulting in the revamping of the Universidad Autónoma de Hidalgo. Today mining forms only a fraction of the municipality’s economy, one cultural aspect that makes Pachuca stand out is the influence that Cornish miners who immigrated here in the 19th century have had. Many of their descendents remain in Pachuca and nearby Real del Monte, as well as two heritages that define the city, football and a dish called “pastes. ”Evidence of early habitation in this area is found in Cerro de las Navajas and Zacualtipán. Here primitive mines to extract green obsidian, arrow heads, scraping tools, an ancient pre-Hispanic obsidian tool-making center has also been found in the small town of San Bartolo near the city. Around 2,000 BCE nomadic groups began to be replaced by sedentary peoples who formed farming villages in an area then known as Itzcuincuitlapilco. Later artifacts from between 200 CE and 850 CE show Teotihuacan influence with platforms and figurines found in San Bartolo, after the Teotihuacan era, the area was dominated by the Chichimecas with their capital in Xaltocan, who called the area around Pachuca Njunthé. Later, the Chichimecas would found the dominion of Cuauhtitlán pushing the native Otomis to the Mezquital Valley and these conquests coalesced into a zone called Cuautlalpan, of which Pachuca was a part. Fortifications in the area of Pachuca city and other areas were built between 1174 and 1181 and this dominion would eventually be overrun by the Aztec Triple Alliance between 1427 and 1430, with rule in Pachuca then coming from the city of Tenochtitlan. According to tradition, it was after this conquest that mineral exploitation began here and in neighboring Real del Monte, the Aztec governing center was where Plaza Juárez in Pachuca city is now. The Spanish arrived here in 1528, killing the local Aztec governor, credit for the Spanish conquest of the Pachuca area has been given Francisco Téllez, an artilleryman who came to Mexico with Hernán Cortés in 1519. He and Gonzalo Rodriguez were the first Spaniards here, constructing two feudal estates, and calling the area Real de Minas de Pachuca. Téllez was also credit for laying out the colonial city of Pachuca on the European model but this story has been proven false
Pachuca
–
Seal
Pachuca
–
Location of Pachuca within Hidalgo
Pachuca
–
Logo
Pachuca
–
Closeup of the Reloj Monumental
10.
Rock (geology)
–
Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a rock, is a combination of the minerals quartz, feldspar. The Earths outer solid layer, the lithosphere, is made of rock, rock has been used by mankind throughout history. The minerals and metals found in rocks have been essential to human civilization, three major groups of rocks are defined, igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is a component of geology. At a granular level, rocks are composed of grains of minerals, the aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed, many rocks contain silica, a compound of silicon and oxygen that forms 74. 3% of the Earths crust. This material forms crystals with other compounds in the rock, the proportion of silica in rocks and minerals is a major factor in determining their name and properties. Rocks are geologically classified according to such as mineral and chemical composition, permeability, the texture of the constituent particles. These physical properties are the end result of the processes that formed the rocks, over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle. These events produce three general classes of rock, igneous, sedimentary, and metamorphic, the three classes of rocks are subdivided into many groups. However, there are no hard and fast boundaries between allied rocks, hence the definitions adopted in establishing rock nomenclature merely correspond to more or less arbitrary selected points in a continuously graduated series. Igneous rock forms through the cooling and solidification of magma or lava and this magma can be derived from partial melts of pre-existing rocks in either a planets mantle or crust. Typically, the melting of rocks is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, igneous rocks are divided into two main categories, plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earths crust, a common example of this type is granite. Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, the chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowens reaction series. Most major igneous rocks are found along this scale, about 64. 7% of the Earths crust by volume consists of igneous rocks, making it the most plentiful category. Of these, 66% are basalts and gabbros, 16% are granite, only 0. 6% are syenites and 0. 3% peridotites and dunites
Rock (geology)
–
Balanced Rock stands in the
Garden of the Gods park in
Colorado Springs
Rock (geology)
–
Rock outcrop along a mountain creek near
Orosí,
Costa Rica.
Rock (geology)
–
Sample of igneous
gabbro
Rock (geology)
–
Sedimentary sandstone with iron oxide bands
11.
Minerals
–
A mineral is a naturally occurring chemical compound, usually of crystalline form and abiogenic in origin. A mineral has one specific chemical composition, whereas a rock can be an aggregate of different minerals or mineraloids, the study of minerals is called mineralogy. There are over 5,300 known mineral species, over 5,070 of these have been approved by the International Mineralogical Association, the silicate minerals compose over 90% of the Earths crust. The diversity and abundance of species is controlled by the Earths chemistry. Silicon and oxygen constitute approximately 75% of the Earths crust, which translates directly into the predominance of silicate minerals, minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various species, changes in the temperature, pressure, or bulk composition of a rock mass cause changes in its minerals. Minerals can be described by their various properties, which are related to their chemical structure. Common distinguishing characteristics include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, tenacity, cleavage, fracture, parting, more specific tests for describing minerals include magnetism, taste or smell, radioactivity and reaction to acid. Minerals are classified by key chemical constituents, the two dominant systems are the Dana classification and the Strunz classification, the silicate class of minerals is subdivided into six subclasses by the degree of polymerization in the chemical structure. All silicate minerals have a unit of a 4− silica tetrahedron—that is, a silicon cation coordinated by four oxygen anions. These tetrahedra can be polymerized to give the subclasses, orthosilicates, disilicates, cyclosilicates, inosilicates, phyllosilicates, other important mineral groups include the native elements, sulfides, oxides, halides, carbonates, sulfates, and phosphates. The first criterion means that a mineral has to form by a natural process, stability at room temperature, in the simplest sense, is synonymous to the mineral being solid. More specifically, a compound has to be stable or metastable at 25 °C, modern advances have included extensive study of liquid crystals, which also extensively involve mineralogy. Minerals are chemical compounds, and as such they can be described by fixed or a variable formula, many mineral groups and species are composed of a solid solution, pure substances are not usually found because of contamination or chemical substitution. Finally, the requirement of an ordered atomic arrangement is usually synonymous with crystallinity, however, crystals are also periodic, an ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form, hardness, and cleavage. There have been recent proposals to amend the definition to consider biogenic or amorphous substances as minerals. The formal definition of an approved by the IMA in 1995, A mineral is an element or chemical compound that is normally crystalline. However, if geological processes were involved in the genesis of the compound, Mineral classification schemes and their definitions are evolving to match recent advances in mineral science
Minerals
–
Amethyst, a variety of
quartz
Minerals
–
Schist is a
metamorphic rock characterized by an abundance of platy minerals. In this example, the rock has prominent
sillimanite porphyroblasts as large as 3 cm (1.2 in).
Minerals
–
Hübnerite, the manganese-rich end-member of the
wolframite series, with minor quartz in the background
Minerals
–
When minerals react, the products will sometimes assume the shape of the reagent; the product mineral is termed to be a pseudomorph of (or after) the reagent. Illustrated here is a pseudomorph of
kaolinite after
orthoclase. Here, the pseudomorph preserved the Carlsbad
twinning common in orthoclase.
12.
Metal
–
A metal is a material that is typically hard, opaque, shiny, and has good electrical and thermal conductivity. Metals are generally malleable—that is, they can be hammered or pressed permanently out of shape without breaking or cracking—as well as fusible and ductile, about 91 of the 118 elements in the periodic table are metals, the others are nonmetals or metalloids. Some elements appear in both metallic and non-metallic forms, astrophysicists use the term metal to collectively describe all elements other than hydrogen and helium, the simplest two, in a star. The star fuses smaller atoms, mostly hydrogen and helium, to larger ones over its lifetime. In that sense, the metallicity of an object is the proportion of its matter made up of all chemical elements. Many elements and compounds that are not normally classified as metals become metallic under high pressures, the atoms of metallic substances are typically arranged in one of three common crystal structures, namely body-centered cubic, face-centered cubic, and hexagonal close-packed. In bcc, each atom is positioned at the center of a cube of eight others, in fcc and hcp, each atom is surrounded by twelve others, but the stacking of the layers differs. Some metals adopt different structures depending on the temperature, atoms of metals readily lose their outer shell electrons, resulting in a free flowing cloud of electrons within their otherwise solid arrangement. This provides the ability of metallic substances to easily transmit heat, while this flow of electrons occurs, the solid characteristic of the metal is produced by electrostatic interactions between each atom and the electron cloud. This type of bond is called a metallic bond, Metals are usually inclined to form cations through electron loss, reacting with oxygen in the air to form oxides over various timescales. Examples,4 Na + O2 →2 Na2O2 Ca + O2 →2 CaO4 Al +3 O2 →2 Al2O3, the transition metals are slower to oxidize because they form a passivating layer of oxide that protects the interior. Others, like palladium, platinum and gold, do not react with the atmosphere at all, some metals form a barrier layer of oxide on their surface which cannot be penetrated by further oxygen molecules and thus retain their shiny appearance and good conductivity for many decades. The oxides of metals are generally basic, as opposed to those of nonmetals, exceptions are largely oxides with very high oxidation states such as CrO3, Mn2O7, and OsO4, which have strictly acidic reactions. Painting, anodizing or plating metals are good ways to prevent their corrosion, however, a more reactive metal in the electrochemical series must be chosen for coating, especially when chipping of the coating is expected. Water and the two form an electrochemical cell, and if the coating is less reactive than the coatee. Metals in general have high conductivity, high thermal conductivity. Typically they are malleable and ductile, deforming under stress without cleaving, in terms of optical properties, metals are shiny and lustrous. Sheets of metal beyond a few micrometres in thickness appear opaque, although most metals have higher densities than most nonmetals, there is wide variation in their densities, lithium being the least dense solid element and osmium the densest
Metal
–
Gallium crystals
Metal
–
Hot metal work from a
blacksmith.
Metal
–
Zinc, a base metal, reacting with an acid
Metal
–
A gold nugget
13.
Mining
–
Mining is extraction of valuable minerals or other geological materials from the earth usually from an orebody, lode, vein, seam, reef or placer deposits. These deposits form a mineralized package that is of economic interest to the miner, ores recovered by mining include metals, coal, oil shale, gemstones, limestone, chalk, dimension stone, rock salt, potash, gravel, and clay. Mining is required to obtain any material that cannot be grown through agricultural processes, Mining in a wider sense includes extraction of any non-renewable resource such as petroleum, natural gas, or even water. Mining of stones and metal has been a human activity since pre-historic times, Mining operations usually create a negative environmental impact, both during the mining activity and after the mine has closed. Hence, most of the nations have passed regulations to decrease the impact. Work safety has long been a concern as well, and modern practices have significantly improved safety in mines, levels of metals recycling are generally low. Unless future end-of-life recycling rates are stepped up, some rare metals may become unavailable for use in a variety of consumer products, due to the low recycling rates, some landfills now contain higher concentrations of metal than mines themselves. Since the beginning of civilization, people have used stone, ceramics and, later and these were used to make early tools and weapons, for example, high quality flint found in northern France, southern England and Poland was used to create flint tools. Flint mines have been found in areas where seams of the stone were followed underground by shafts. The mines at Grimes Graves and Krzemionki are especially famous, other hard rocks mined or collected for axes included the greenstone of the Langdale axe industry based in the English Lake District. The oldest-known mine on archaeological record is the Lion Cave in Swaziland, at this site Paleolithic humans mined hematite to make the red pigment ochre. Mines of an age in Hungary are believed to be sites where Neanderthals may have mined flint for weapons. Ancient Egyptians mined malachite at Maadi, at first, Egyptians used the bright green malachite stones for ornamentations and pottery. Later, between 2613 and 2494 BC, large building projects required expeditions abroad to the area of Wadi Maghareh in order to secure minerals and other resources not available in Egypt itself. Quarries for turquoise and copper were found at Wadi Hammamat, Tura, Aswan and various other Nubian sites on the Sinai Peninsula. Mining in Egypt occurred in the earliest dynasties, the gold mines of Nubia were among the largest and most extensive of any in Ancient Egypt. These mines are described by the Greek author Diodorus Siculus, who mentions fire-setting as one used to break down the hard rock holding the gold. One of the complexes is shown in one of the earliest known maps, the miners crushed the ore and ground it to a fine powder before washing the powder for the gold dust
Mining
–
Surface
coal mining
Mining
–
Chalcolithic copper mine in
Timna Valley,
Negev Desert
Mining
–
Ancient Roman development of the
Dolaucothi Gold Mines, Wales
Mining
–
Agricola, author of
De Re Metallica
14.
Smelting
–
Smelting is a form of extractive metallurgy, its main use is to produce a base metal from its ore. This includes production of silver, iron, copper and other metals from their ores. Smelting makes use of heat and a reducing agent to decompose the ore, driving off other elements as gases or slag. The reducing agent is commonly a source of such as coke. The carbon removes oxygen from the ore, leaving behind the elemental metal, the carbon is thus oxidized in two stages, producing first carbon monoxide and then carbon dioxide. As most ores are impure, it is necessary to use flux, such as limestone. Plants for the reduction of aluminium are also generally referred to as aluminium smelters. Smelting involves more than just melting the metal out of its ore, most ores are a chemical compound of the metal with other elements, such as oxygen, sulfur or carbon and oxygen together. To produce the metal, these compounds have to undergo a chemical reaction, smelting therefore consists of using suitable reducing substances that will combine with those oxidizing elements to free the metal. In the case of carbonates and sulfides, a process called roasting drives out the carbon or sulfur, leaving an oxide. Roasting is usually carried out in an oxidizing environment, a few practical examples, Malachite, a common ore of copper, is primarily copper carbonate hydroxide Cu22. This mineral undergoes thermal decomposition to 2CuO, CO2, and H2O in several stages between 250 °C and 350 °C, the carbon dioxide and water are expelled into the atmosphere, leaving copper oxide which can be directly reduced to copper as described in the following section titled Reduction. Galena, the most common mineral of lead, is primarily lead sulfide, the sulfide is oxidized to a sulfite which thermally decomposes into lead oxide and sulfur dioxide gas. The sulfur dioxide is expelled, and the oxide is reduced as below. Reduction is the final, high-temperature step in smelting and it is here that the oxide becomes the elemental metal. A reducing environment pulls the final oxygen atoms from the raw metal, the required temperature varies over a very large range, both in absolute terms and in terms of the melting point of the base metal. Fluxes are used in smelting for several purposes, chief among them catalyzing the desired reactions, of the seven metals known in antiquity, only gold occurred regularly in native form in the natural environment. The others – copper, lead, silver, tin, iron and mercury – occur primarily as minerals and these minerals are primarily carbonates, sulfides, or oxides of the metal, mixed with other components such as silica and alumina
Smelting
–
Electric phosphate smelting furnace in a
TVA chemical plant (1942)
Smelting
–
Casting bronze ding-tripods, from the Chinese Tiangong Kaiwu encyclopedia of
Song Yingxing, published in 1637.
Smelting
–
Cowles Syndicate of
Ohio in
Stoke-upon-Trent England, late 1880s.
British Aluminium used the process of
Paul Héroult about this time.
15.
Mineral
–
A mineral is a naturally occurring chemical compound, usually of crystalline form and abiogenic in origin. A mineral has one specific chemical composition, whereas a rock can be an aggregate of different minerals or mineraloids, the study of minerals is called mineralogy. There are over 5,300 known mineral species, over 5,070 of these have been approved by the International Mineralogical Association, the silicate minerals compose over 90% of the Earths crust. The diversity and abundance of species is controlled by the Earths chemistry. Silicon and oxygen constitute approximately 75% of the Earths crust, which translates directly into the predominance of silicate minerals, minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various species, changes in the temperature, pressure, or bulk composition of a rock mass cause changes in its minerals. Minerals can be described by their various properties, which are related to their chemical structure. Common distinguishing characteristics include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, tenacity, cleavage, fracture, parting, more specific tests for describing minerals include magnetism, taste or smell, radioactivity and reaction to acid. Minerals are classified by key chemical constituents, the two dominant systems are the Dana classification and the Strunz classification, the silicate class of minerals is subdivided into six subclasses by the degree of polymerization in the chemical structure. All silicate minerals have a unit of a 4− silica tetrahedron—that is, a silicon cation coordinated by four oxygen anions. These tetrahedra can be polymerized to give the subclasses, orthosilicates, disilicates, cyclosilicates, inosilicates, phyllosilicates, other important mineral groups include the native elements, sulfides, oxides, halides, carbonates, sulfates, and phosphates. The first criterion means that a mineral has to form by a natural process, stability at room temperature, in the simplest sense, is synonymous to the mineral being solid. More specifically, a compound has to be stable or metastable at 25 °C, modern advances have included extensive study of liquid crystals, which also extensively involve mineralogy. Minerals are chemical compounds, and as such they can be described by fixed or a variable formula, many mineral groups and species are composed of a solid solution, pure substances are not usually found because of contamination or chemical substitution. Finally, the requirement of an ordered atomic arrangement is usually synonymous with crystallinity, however, crystals are also periodic, an ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form, hardness, and cleavage. There have been recent proposals to amend the definition to consider biogenic or amorphous substances as minerals. The formal definition of an approved by the IMA in 1995, A mineral is an element or chemical compound that is normally crystalline. However, if geological processes were involved in the genesis of the compound, Mineral classification schemes and their definitions are evolving to match recent advances in mineral science
Mineral
–
Amethyst, a variety of
quartz
Mineral
–
Schist is a
metamorphic rock characterized by an abundance of platy minerals. In this example, the rock has prominent
sillimanite porphyroblasts as large as 3 cm (1.2 in).
Mineral
–
Hübnerite, the manganese-rich end-member of the
wolframite series, with minor quartz in the background
Mineral
–
When minerals react, the products will sometimes assume the shape of the reagent; the product mineral is termed to be a pseudomorph of (or after) the reagent. Illustrated here is a pseudomorph of
kaolinite after
orthoclase. Here, the pseudomorph preserved the Carlsbad
twinning common in orthoclase.
16.
Extractive metallurgy
–
Extractive metallurgy is a branch of metallurgical engineering wherein process and methods of extraction of metals from their natural mineral deposits are studied. Several processes are used for extraction of same metal depending on occurrence, thereafter, the ore is physically separated from any unwanted impurity, depending on the form of occurrence and/or further process involved. Separation processes take advantage of properties of the materials. These physical properties can include density, particle size and shape, electrical and magnetic properties, and surface properties. This concentrate is either processed to remove moisture or else used as is for extraction of the metal or made into shapes and forms that can undergo further processing. Ore bodies often contain more than one valuable metal, tailings of a previous process may be used as a feed in another process to extract a secondary product from the original ore. Additionally, a concentrate may contain more than one valuable metal and that concentrate would then be processed to separate the valuable metals into individual constituents. Hydrometallurgy is concerned with processes involving aqueous solutions to extract metals from ores, the first step in the hydrometallurgical process is leaching, which involves dissolution of the valuable metals into the aqueous solution and /or a suitable solvent. This may include precipitation, distillation, adsorption, and solvent extraction, the final recovery step may involve precipitation, cementation, or an electrometallurgical process. Sometimes, hydrometallurgical processes may be carried out directly on the ore material without any pretreatment steps, more often, the ore must be pretreated by various mineral processing steps, and sometimes by pyrometallurgical processes. Pyrometallurgy involves high temperature processes where chemical reactions take place among gases, solids, solids containing valuable metals are treated to form intermediate compounds for further processing or converted into their elemental or metallic state. Pyrometallurgical processes that involve gases and solids are typified by calcining and roasting operations, processes that produce molten products are collectively referred to as smelting operations. The energy required to sustain the high temperature pyrometallurgical processes may derive from the nature of the chemical reactions taking place. Typically, these reactions are oxidation, e. g. of sulfide to sulfur dioxide, often, however, energy must be added to the process by combustion of fuel or, in the case of some smelting processes, by the direct application of electrical energy. Ellingham Diagrams are a way of analysing the possible reactions. Electrometallurgy involves metallurgical processes that take place in form of electrolytic cell. The most common types of processes are electrowinning and electro-refining. Electrowinning is a process used to recover metals in aqueous solution
Extractive metallurgy
–
Ellingham diagram for high temperature oxidation
17.
Oxide
–
An oxide /ˈɒksaɪd/ is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. Oxide itself is the dianion of oxygen, an O2– atom, Metal oxides thus typically contain an anion of oxygen in the oxidation state of −2. Most of the Earths crust consists of oxides, the result of elements being oxidized by the oxygen in air or in water. Hydrocarbon combustion affords the two principal carbon oxides, carbon monoxide and carbon dioxide, even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a skin of Al2O3 that protects the foil from further corrosion. Individual elements can form multiple oxides, each containing different amounts of the element. Certain elements can form many different oxides, such those of nitrogen, due to its electronegativity, oxygen forms stable chemical bonds with almost all elements to give the corresponding oxides. Noble metals are prized because they resist direct chemical combination with oxygen, two independent pathways for corrosion of elements are hydrolysis and oxidation by oxygen. The combination of water and oxygen is even more corrosive, virtually all elements burn in an atmosphere of oxygen, or an oxygen rich environment. In the presence of water and oxygen, some elements— sodium—react rapidly, even dangerously, in part for this reason, alkali and alkaline earth metals are not found in nature in their metallic, i. e. native, form. Caesium is so reactive with oxygen that it is used as a getter in vacuum tubes, the surface of most metals consists of oxides and hydroxides in the presence of air. A well-known example is aluminium foil, which is coated with a film of aluminium oxide that passivates the metal. The aluminium oxide layer can be built to greater thickness by the process of electrolytic anodising, though solid magnesium and aluminium react slowly with oxygen at STP—they, like most metals, burn in air, generating very high temperatures. Finely grained powders of most metals can be explosive in air. Consequently, they are used in Solid-fuel rockets. In dry oxygen, iron forms iron oxide, but the formation of the hydrated ferric oxides, Fe2O3−x2x. Free oxygen production by photosynthetic bacteria some 3.5 billion years ago precipitated iron out of solution in the oceans as Fe2O3 in the important iron ore hematite. Oxides have a range of different structures, from molecules to polymeric
Oxide
–
Oxides, such as
iron(III) oxide or
rust, which consists of hydrated
iron(III) oxides Fe 2 O 3 · n H 2 O and
iron(III) oxide-hydroxide (FeO(OH), Fe(OH) 3), form when oxygen combines with other elements
Oxide
–
Silicon dioxide (SiO 2) is one of the most common oxides on the surface of earth. Like most oxides, it adopts a polymeric structure.
18.
Silicate minerals
–
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of rock-forming minerals and they are classified based on the structure of their silicate groups, which contain different ratios of silicon and oxygen. Nesosilicates, or orthosilicates, have the orthosilicate ion, which constitute isolated 4− tetrahedra that are connected only by interstitial cations and these exist as 3-member 6− and 6-member 12− rings, where T stands for a tetrahedrally coordinated cation. Inosilicates, or chain silicates, have interlocking chains of silicate tetrahedra with either SiO3,1,3 ratio, for single chains or Si4O11,4,11 ratio, for double chains. Nickel–Strunz classification,09. D Pyroxene group Enstatite – orthoferrosilite series Enstatite – MgSiO3 Ferrosilite – FeSiO3 Pigeonite – Ca0.251, all phyllosilicate minerals are hydrated, with either water or hydroxyl groups attached. Serpentine subgroup Antigorite – Mg3Si2O54 Chrysotile – Mg3Si2O54 Lizardite – Mg3Si2O54 Clay minerals group Halloysite – Al2Si2O54 Kaolinite – Al2Si2O54 Illite – 24O10 Montmorillonite –0 and this group comprises nearly 75% of the crust of the Earth. Tectosilicates, with the exception of the group, are aluminosilicates. Nickel–Strunz classification,09. F and 09. G,04. A, an introduction to the rock-forming minerals. Wise, W. S. Zussman, J. Rock-forming minerals, P.982 pp. Hurlbut, Cornelius S. Danas Manual of Mineralogy. Mindat. org, Dana classification Webmineral, Danas New Silicate Classification Media related to Silicates at Wikimedia Commons
Silicate minerals
–
Copper silicate mineral
chrysocolla
Silicate minerals
–
Nesosilicate specimens at the Museum of Geology in South Dakota
Silicate minerals
–
Kyanite crystals (unknown scale)
Silicate minerals
–
Sorosilicate exhibit at Museum of Geology in South Dakota
19.
Native copper
–
Native copper is an uncombined form of copper which occurs as a natural mineral. Copper is one of the few elements to occur in native form, although it most commonly occurs in oxidized states. Native copper was an important ore of copper in historic times and was used by pre-historic peoples, native copper occurs rarely as isometric cubic and octahedral crystals, but more typically as irregular masses and fracture fillings. It has a reddish, orangish, and/or brownish color on fresh surfaces and its specific gravity is 8.9 and its hardness is 2. 5–3. The mines of the Keweenaw native copper deposits of Upper Michigan were major producers in the 19th and early 20th centuries. The first commercial mines in the Keweenaw Peninsula opened in the 1840s, isle Royale in western Lake Superior was also a site of many tons of native copper. Some of it was extracted by native peoples, but only one of several attempts at mining turned a profit there. Another major native copper deposit is in Coro Coro, Bolivia, the name copper comes from the Greek kyprios, of Cyprus, the location of copper mines since pre-historic times
Native copper
–
Native copper from Ray mine, Arizona (specimen 5.25 x 4 x 1 cm)
20.
Earth
–
Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely, over 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost always appears in lowercase in colloquial expressions such as what on earth are you doing, the oldest material found in the Solar System is dated to 4. 5672±0.0006 billion years ago. By 4. 54±0.04 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun
Earth
–
"
The Blue Marble " photograph of Earth, taken during the
Apollo 17 lunar mission in 1972
Earth
–
Artist's impression of the early Solar System's planetary disk
Earth
–
World map color-coded by relative height
Earth
–
The summit of
Chimborazo, in Ecuador, is the point on Earth's surface farthest from its center.
21.
Crust (geology)
–
In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle. The crust of the Earth is composed of a variety of igneous, metamorphic. The crust is underlain by the mantle, the upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity, the crust occupies less than 1% of Earths volume. The crust of the Earth is of two types, oceanic and continental. The oceanic crust is 5 km to 10 km thick and is composed primarily of basalt, diabase, the continental crust is typically from 30 km to 50 km thick and is mostly composed of slightly less dense rocks than those of the oceanic crust. Some of these less dense rocks, such as granite, are common in the continental crust, both the continental and oceanic crust float on the mantle. Because the continental crust is thicker, it both to greater elevations and greater depth than the oceanic crust. The slightly lower density of continental rock compared to basaltic oceanic rock contributes to the higher relative elevation of the top of the continental crust. As the top of the continental crust reaches elevations higher than that of the oceanic, the temperature of the crust increases with depth, reaching values typically in the range from about 200 °C to 400 °C at the boundary with the underlying mantle. The crust and underlying relatively rigid uppermost mantle make up the lithosphere, because of convection in the underlying plastic upper mantle and asthenosphere, the lithosphere is broken into tectonic plates that move. The temperature increases by as much as 30 °C for every kilometer locally in the part of the crust. Earth has probably always had some form of basaltic crust, in contrast, the bulk of the continental crust is much older. The oldest continental crustal rocks on Earth have ages in the range from about 3.7 to 4, some zircon with age as great as 4.3 billion years has been found in the Narryer Gneiss Terrane. The average age of the current Earths continental crust has been estimated to be about 2.0 billion years, most crustal rocks formed before 2.5 billion years ago are located in cratons. Such old continental crust and the underlying mantle asthenosphere are less dense than elsewhere in Earth, formation of new continental crust is linked to periods of intense orogeny, these periods coincide with the formation of the supercontinents such as Rodinia, Pangaea and Gondwana. The continental crust has a composition similar to that of andesite. The most abundant minerals in Earths continental crust are feldspars, which make up about 41% of the crust by weight, followed by quartz at 12%, Continental crust is enriched in incompatible elements compared to the basaltic ocean crust and much enriched compared to the underlying mantle
Crust (geology)
–
Shield
22.
Geology
–
Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, and the processes by which they change over time. Geology can also refer generally to the study of the features of any terrestrial planet. Geology gives insight into the history of the Earth by providing the evidence for plate tectonics, the evolutionary history of life. Geology also plays a role in engineering and is a major academic discipline. The majority of data comes from research on solid Earth materials. These typically fall into one of two categories, rock and unconsolidated material, the majority of research in geology is associated with the study of rock, as rock provides the primary record of the majority of the geologic history of the Earth. There are three types of rock, igneous, sedimentary, and metamorphic. The rock cycle is an important concept in geology which illustrates the relationships between three types of rock, and magma. When a rock crystallizes from melt, it is an igneous rock, the sedimentary rock can then be subsequently turned into a metamorphic rock due to heat and pressure and is then weathered, eroded, deposited, and lithified, ultimately becoming a sedimentary rock. Sedimentary rock may also be re-eroded and redeposited, and metamorphic rock may also undergo additional metamorphism, all three types of rocks may be re-melted, when this happens, a new magma is formed, from which an igneous rock may once again crystallize. Geologists also study unlithified material which typically comes from more recent deposits and these materials are superficial deposits which lie above the bedrock. Because of this, the study of material is often known as Quaternary geology. This includes the study of sediment and soils, including studies in geomorphology, sedimentology and this theory is supported by several types of observations, including seafloor spreading, and the global distribution of mountain terrain and seismicity. This coupling between rigid plates moving on the surface of the Earth and the mantle is called plate tectonics. The development of plate tectonics provided a basis for many observations of the solid Earth. Long linear regions of geologic features could be explained as plate boundaries, mid-ocean ridges, high regions on the seafloor where hydrothermal vents and volcanoes exist, were explained as divergent boundaries, where two plates move apart. Arcs of volcanoes and earthquakes were explained as convergent boundaries, where one plate subducts under another, transform boundaries, such as the San Andreas Fault system, resulted in widespread powerful earthquakes. Plate tectonics also provided a mechanism for Alfred Wegeners theory of continental drift and they also provided a driving force for crustal deformation, and a new setting for the observations of structural geology
Geology
–
On this diagram, subducting
slabs are in blue, and continental margins and a few plate boundaries are in red. The blue blob in the cutaway section is the seismically imaged
Farallon Plate, which is subducting beneath North America. The remnants of this plate on the Surface of the Earth are the
Juan de Fuca Plate and Explorer plate in the Northwestern USA / Southwestern Canada, and the
Cocos Plate on the west coast of Mexico.
Geology
–
This schematic diagram of the rock cycle shows the relationship between magma and sedimentary, metamorphic, and igneous rock
Geology
Geology
–
Geologic cross-section of
Kittatinny Mountain. This cross-section shows metamorphic rocks, overlain by younger sediments deposited after the metamorphic event. These rock units were later folded and faulted during the uplift of the mountain.
23.
Ore genesis
–
Various theories of ore genesis explain how the various types of mineral deposits form within the Earths crust. Ore-genesis theories vary depending on the mineral or commodity examined, ore-genesis theories generally involve three components, source, transport or conduit, and trap. Source is required because metal must come from somewhere, and be liberated by some process, trapping is required to concentrate the metal via some physical, chemical, or geological mechanism into a concentration which forms mineable ore. The biggest deposits form when the source is large, the mechanism is efficient. Fractional crystallization, separates ore and non-ore minerals according to their crystallization temperature, as early crystallizing minerals form from magma, they incorporate certain elements, some of which are metals. These crystals may settle onto the bottom of the intrusion, concentrating ore minerals there, chromite and magnetite are ore minerals that form in this way. Liquid immiscibility, sulfide ores containing copper, nickel, or platinum may form from this process, as a magma changes, parts of it may separate from the main body of magma. Two liquids that will not mix are called immiscible, oil, in magmas, sulfides may separate and sink below the silicate-rich part of the intrusion or be injected into the rock surrounding it. These deposits are found in mafic and ultramafic rocks and these processes are the physicochemical phenomena and reactions caused by movement of hydrothermal water within the crust, often as a consequence of magmatic intrusion or tectonic upheavals. The foundations of hydrothermal processes are the source-transport-trap mechanism, metal sources may include a plethora of rocks. However most metals of economic importance are carried as trace elements within rock-forming minerals and this happens because of, incompatibility of the metal with its host mineral, for example zinc in calcite, which favours aqueous fluids in contact with the host mineral during diagenesis. These metal-bearing complexes facilitate transport of metals within aqueous solutions, generally as hydroxides and this process is especially well understood in gold metallogeny where various thiosulfate, chloride, and other gold-carrying chemical complexes. The majority of deposits formed by hydrothermal processes include sulfide minerals. This may occur without much hydrothermal fluid flow, and this is typical of podiform chromite deposits, metamorphic processes also control many physical processes which form the source of hydrothermal fluids, outlined above. Surficial processes are the physical and chemical phenomena which cause concentration of ore material within the regolith and this includes placer deposits, laterite deposits, and residual or eluvial deposits. Ore deposits rarely fit neatly into the categories in which geologists wish to place them, many may be formed by one or more of the basic genesis processes above, creating ambiguous classifications and much argument and conjecture. Often ore deposits are classified after examples of their type, for instance Broken Hill type lead-zinc-silver deposits or Carlin–type gold deposits and this scheme, proposed by Waldemar Lindgren classified hydrothermal deposits as hypothermal, mesothermal, epithermal, and telethermal. Epithermal deposits are hydrothermal ore deposits formed at low temperatures near the Earth´s surface, that fill veins, breccias, the age of formation of epithermal deposits in México is currently being investigated
Ore genesis
–
High-grade gold ore from the Harvard Mine,
Jamestown, California, a wide quartz-gold vein in California's
Mother Lode. Specimen is 3.2 cm wide.
Ore genesis
–
High-grade (bonanza) gold ore, brecciated quartz-adularia rhyolite.
Native gold (Au) occurs in this rock as colloform bands, partially replaces breccia clasts, and is also disseminated in the matrix. Published research indicates that Sleeper Mine rocks represent an ancient
epithermal gold deposit (hot springs gold deposit), formed by volcanism during Basin & Range
extensional tectonics. Sleeper Mine,
Humboldt County, Nevada.
Ore genesis
–
Citrobacter species can have concentrations of uranium in their bodies 300 times higher than in the surrounding environment.
Ore genesis
–
Tunicates such as this bluebell tunicate contain vanadium as
vanabin.
24.
Mineral resource classification
–
Mineral resource classification is the classification of mineral resources based on an increasing level of geological knowledge and confidence. Mineral deposits can be classified as, Mineral resources that are potentially valuable, classification, because it is an economic function, is governed by statutes, regulations and industry best practice norms. G. Dill are the general standards, Mineral Resources are further sub-divided, in order of increasing geological confidence, into inferred, Indicated and measured Categories. Inferred Mineral Resource is the part of a resource for which tonnage, grade. It is inferred from geological evidence and assumed but not verified geological or grade continuity, Mineral reserves are resources known to be economically feasible for extraction. Reserves are either Probable Reserves or Proved Reserves, a Probable Ore Reserve is the part of indicated, and in some circumstances, measured mineral resources that can be mined in an economically viable fashion. It includes diluting material and allowances for losses which may occur when the material is mined, a Probable Ore Reserve has a lower level of confidence than a Proved Ore Reserve but is of sufficient quality to serve as the basis for decision on the development of deposit. A Proved Ore Reserve is the part of Measured resources that can be mined in a viable fashion. It includes diluting materials and allowances for losses which occur when the material is mined, a Proved Ore Reserve represents the highest confidence category of reserve estimate. The style of mineralization or other factors could mean that Proved Ore Reserves are not achievable in some deposits. S
Mineral resource classification
–
A "
McKelvey diagram" showing the relation of mineral resource classifications to economics and geologic certainty.
25.
Golden Mile (Kalgoorlie)
–
The town was founded in 1893 during the Coolgardie gold rush, and is located close to the so-called Golden Mile. It is also the destination of the Goldfields Water Supply Scheme. At June 2015, Kalgoorlie, had an urban population of 32,797. The name Kalgoorlie is derived from the Wangai word Karlkurla, meaning place of the silky pears, in January 1893, prospectors Patrick Hannan, Tom Flanagan, and Dan OShea were travelling to Mount Youle when one of their horses cast a shoe. During the halt in their journey, the men noticed signs of gold in the area and decided to stay and investigate. On 17 June 1893, Hannan filed a Reward Claim, leading to hundreds of men swarming to the area in search of gold and Kalgoorlie, the population of the town was 2,018 in 1898. The concentrated area of gold mines surrounding the original Hannans find is often referred to as the Golden Mile. In 1901 the population of Kalgoorlie was 4,793 which increased to 6,790 by 1903, the standardisation of the railway connecting Perth in 1968 completed the Sydney–Perth railway, making rail travel from Perth to Sydney possible, the Indian Pacific rail service commenced soon after. During the 1890s, the Goldfields area boomed as a whole, with a population exceeding 200,000. The area gained a reputation for being a wild west with bandits. Places, famous or infamous, that Kalgoorlie is noted for include its water pipeline and its main street is Hannan Street, named after the towns founder. One of the infamous brothels also serves as a museum and is a national attraction. Kalgoorlie and the district was serviced by an extensive collection of suburban railways and tramways. On 20 April 2010, Kalgoorlie was shaken by a an earthquake that reached 5.0 on the richter scale, the epicentre was 30 km north east of the town. The quake caused damage to a number of hotels and historic buildings along Burt Street in Boulder. The entire Burt St. precinct was evacuated until 23 April, work in the Superpit and many other mines around Kalgoorlie was stopped. Two people suffered injuries as a result of the quake. Several police officers were injured during the riot and at least ten people were charged, Kalgoorlie–Boulder is a regional centre and has a Chamber of Commerce and a Chamber of Minerals and Energy
Golden Mile (Kalgoorlie)
–
Kalgoorlie Post Office, Hannan Street
Golden Mile (Kalgoorlie)
–
Kalgoorlie Gold. Display at
South Australia Museum.
Golden Mile (Kalgoorlie)
–
Hannan St in September 1930. The Exchange Hotel is at the centre, with the Palace Hotel on the right.
Golden Mile (Kalgoorlie)
–
Kalgoorlie after the 1934
race riots
26.
Kalgoorlie
–
The town was founded in 1893 during the Coolgardie gold rush, and is located close to the so-called Golden Mile. It is also the destination of the Goldfields Water Supply Scheme. At June 2015, Kalgoorlie, had an urban population of 32,797. The name Kalgoorlie is derived from the Wangai word Karlkurla, meaning place of the silky pears, in January 1893, prospectors Patrick Hannan, Tom Flanagan, and Dan OShea were travelling to Mount Youle when one of their horses cast a shoe. During the halt in their journey, the men noticed signs of gold in the area and decided to stay and investigate. On 17 June 1893, Hannan filed a Reward Claim, leading to hundreds of men swarming to the area in search of gold and Kalgoorlie, the population of the town was 2,018 in 1898. The concentrated area of gold mines surrounding the original Hannans find is often referred to as the Golden Mile. In 1901 the population of Kalgoorlie was 4,793 which increased to 6,790 by 1903, the standardisation of the railway connecting Perth in 1968 completed the Sydney–Perth railway, making rail travel from Perth to Sydney possible, the Indian Pacific rail service commenced soon after. During the 1890s, the Goldfields area boomed as a whole, with a population exceeding 200,000. The area gained a reputation for being a wild west with bandits. Places, famous or infamous, that Kalgoorlie is noted for include its water pipeline and its main street is Hannan Street, named after the towns founder. One of the infamous brothels also serves as a museum and is a national attraction. Kalgoorlie and the district was serviced by an extensive collection of suburban railways and tramways. On 20 April 2010, Kalgoorlie was shaken by a an earthquake that reached 5.0 on the richter scale, the epicentre was 30 km north east of the town. The quake caused damage to a number of hotels and historic buildings along Burt Street in Boulder. The entire Burt St. precinct was evacuated until 23 April, work in the Superpit and many other mines around Kalgoorlie was stopped. Two people suffered injuries as a result of the quake. Several police officers were injured during the riot and at least ten people were charged, Kalgoorlie–Boulder is a regional centre and has a Chamber of Commerce and a Chamber of Minerals and Energy
Kalgoorlie
–
Kalgoorlie Post Office, Hannan Street
Kalgoorlie
–
Kalgoorlie Gold. Display at
South Australia Museum.
Kalgoorlie
–
Hannan St in September 1930. The Exchange Hotel is at the centre, with the Palace Hotel on the right.
Kalgoorlie
–
Kalgoorlie after the 1934
race riots
27.
Conglomerate (geology)
–
Conglomerates form by the consolidation and lithification of gravel. The size and composition of the fraction of a conglomerate may or may not vary in composition, sorting. In some conglomerates, the gravel-size class consist almost entirely of what were clay clasts at the time of deposition, conglomerates can be found in sedimentary rock sequences of all ages but probably make up less than 1 percent by weight of all sedimentary rocks. A sedimentary rock composed largely of gravel is first named according to the roundness of the gravel, if the gravel clasts that comprise it is largely well-rounded to subrounded, it is a conglomerate. If the gravel clasts that comprise it are largely angular, it is a breccia, such breccias can be called sedimentary breccias to differentiate them from other types of breccia, e. g. volcanic and fault breccias. Sedimentary rocks that contain a mixture of rounded and angular gravel clasts are sometimes called breccio-conglomerate, conglomerates are rarely composed entirely of gravel-size clasts. Typically, the space between the gravel-size clasts is filled by a mixture composed of varying amounts of silt, sand, paraconglomerates are also often unstratified and can contain more matrix than gravel clasts. If the gravel clasts of a conglomerate are in contact with each other, unlike paraconglomerates, orthoconglomerates are typically cross-bedded and often well-cemented and lithified by either calcite, hematite, quartz, or clay. The differences between paraconglomerates and orthoconglomerates reflect differences in how they are deposited, paraconglomerates are commonly either glacial tills or debris flow deposits. Orthoconglomerates are typically associated with aqueous currents, conglomerates are also classified according to the composition of their clasts. A conglomerate or any clastic sedimentary rock that consists of a rock or mineral is known as either a monomict, monomictic, oligomict. If the conglomerate consists of two or more different types of rocks, minerals, or combination of both, it is known as either a polymict or polymictic conglomerate. If a polymictic conglomerate contains an assortment of the clasts of metastable and unstable rocks and minerals, two recognized types of type of intraformational conglomerates are shale-pebble and flat-pebble conglomerates. Finally, conglomerates are often differentiated and named according to the dominant clast size comprising them, conglomerates are deposited in a variety of sedimentary environments. In turbidites, the part of a bed is typically coarse-grained. In this setting, conglomerates are normally very well sorted, well-rounded, conglomerates are normally present at the base of sequences laid down during marine transgressions above an unconformity, and are known as basal conglomerates. They represent the position of the shoreline at a time and are diachronous. Conglomerates deposited in environments are typically well rounded and well sorted
Conglomerate (geology)
–
Boulder of conglomerate with cobble-sized clasts. Rock hammer for scale.
Conglomerate (geology)
–
Carmelo Formation (Conglomerate) at
Point Lobos
Conglomerate (geology)
–
A conglomerate at the base of the
Cambrian in the Black Hills, South Dakota.
Conglomerate (geology)
–
Section of polymict conglomerate from offshore rock
core,
Alaska, approximate depth 10,000 ft.
28.
Elliot Lake
–
Elliot Lake is a city in Algoma District, Ontario, Canada. It is north of Lake Huron, midway between the cities of Sudbury and Sault Ste, marie in the Northern Ontario region. Prior to the settlement of the city, an Ojibwa village existed near the present hospital site on the lakes shoreline. The city was established as a community for the mining industry in 1955 after the discovery of uranium in the area. By the late 1950s, its population had grown to about 25,000 and it was originally incorporated as an improvement district. Geologist Franc Joubin and American financier Joseph Hirshhorn were instrumental in its founding, the principal mining companies were Denison Mines and Rio Algom. The population has varied with several boom-and-bust cycles from the 1950s to the 1990s, in 1959, the United States declared that it would buy no more uranium from Canada after 1962. During the 1970s, federal plans for CANDU Reactors and Ontario Hydros interest in energy led the town, anticipating a population of 30,000. However, by the early 1990s depleted reserves and low prices caused the last mines in the area to close, Elliot Lake was incorporated as a city in 1990. In the years since, the city looked elsewhere for its survival, finding some success promoting itself as a retirement community and tourist destination. In the late 2000s, mineral exploration began taking place in the area, on June 23,2012, part of a roof collapsed at Algo Centre Mall, sending metal and concrete debris crashing down through two floors of the shopping centre. Pearson Plaza is under construction, set for a late 2016 open, stanleigh Mine, operated by Rio Algom Ltd. produced 14 million tons of ore. Spanish American Mine, operated by Rio Algom Ltd. produced 79,000 tons of ore, can-Met Mine, operated by Denison Mines Ltd. produced 2.6 million tons of ore. Milliken Mine, operated by Rio Algom Ltd. produced 6.3 million tons of ore, panel Mine, operated by Rio Algom Ltd. produced 15 million tons of ore. Denison Mine, operated by Denison Mines Ltd. produced 69 million tons of ore, stanrock Mine, operated by Denison Mines Ltd. produced 6.4 million tons of ore. Quirke Mine, operated by Rio Algom Ltd. produced 44 million tons of ore, pronto Mine, operated by Rio Algom Ltd. produced 2.3 million tons of ore. Buckles Mine, operated by Rio Algom Ltd. produced 276,000 tons of ore, lacnor Mine Lake Nordic, operated by Rio Algom Ltd. produced 3.4 million tons of ore. Nordic Mine, operated by Rio Algom Ltd. produced 13 million tons of ore, in 1974, uranium miners in Elliot Lake became alarmed about the high incidence of lung cancer and silicosis, and they went on strike over health and safety conditions
Elliot Lake
–
The city of Elliot Lake; the lake on the right
Elliot Lake
–
Mount Dufour ski hill
29.
Witwatersrand
–
The Witwatersrand aka The Reef, is a 56-kilometre-long north-facing scarp in the Gauteng Province of South Africa. This east–west-running scarp can be traced with only one short gap from Bedfordview in the east, through Johannesburg and Roodepoort, the scarp forms the northern edge of a 7- to 10-kilometre-wide plateau which rises about 200 m above the surrounding plains of the Highveld. The entire plateau-like structure is often called the “Witwatersrand”. The plateau’s elevation above sea-level is between 1700–1800 m, the Witwatersrand lies within the province of Gauteng, formerly called the “PWV”, an abbreviation for Pretoria, Witwatersrand and Vereeniging. When used in this context, the term Witwatersrand refers to the entire Greater Johannesburg Metropolitan Area. This conurbation is oblong in shape and runs from Springs in the east to Randfontein and Carletonville in the west and this area is also often colloquially referred to as “the Rand” or “Wits”. Because of the quantities of gold that have been extracted from the Witwatersrand rocks. The Witwatersrand plateau consists of a 5000- to 7000-metre-thick layer of sedimentary rocks laid down over a period of about 260 million years. The oldest rocks form the northern scarp of the Witwatersrand plateau, Gold is found in the conglomerate strata of the younger members of the Supergroup. The abundance of gold is without equal anywhere else in the world. Over 50000 tons have been mined from these rocks since this precious metal was first discovered here in 1886 and this accounts for approximately 50% of all the gold ever mined on earth. The gold-bearing conglomerates occur chiefly in the upper, younger layers of the Witwatersrand Supergroup of rocks, the Witwatersrand Supergroup strata which reach the surface in Johannesburg dip downwards to the south at an angle of about 30°. From there on they are almost everywhere, with few exceptions. Gold mining in these buried portions of the Witwatersrand Supergroup is sometimes carried out at depths of 4 kilometres below the surface, the Kaapvaal Craton, one of the first microcontinents to form on Earth through plate tectonics, was assembled about 3900 million years ago. Its size and position relative to Southern Africa today is indicated in the diagram on the left, about 3000 million years ago local cooling of the underlying asthenosphere caused subsidence of the south-eastern portion of this microcontinent below sea level. The floor of newly formed “Witwatersrand sea” consisted of smoothly eroded granites. Sandy sediments brought in by rivers from the north started being deposited on the granite about 2970 million years ago and this sandy layer eventually became compressed to form the Orange Grove Quartzite, the lowermost layer of the Witwatersrand Supergroup. This quartzite formation forms the scarp from which the Witwatersrand derives its name, as the sea deepened finer grained and muddy sediments accumulated
Witwatersrand
–
Waterfall in the
Walter Sisulu National Botanical Garden, formerly the Witwatersrand National Botanical Gardens. Waterfalls like this, cascading over a 56-kilometre-long (35 mi)
quartzite ridge in Gauteng gave rise to the name “Witwatersrand”, which means “white water ridge” in
Afrikaans.
Witwatersrand
Witwatersrand
Witwatersrand
–
The street entrance of George Harrison Park
30.
South Africa
–
South Africa, officially the Republic of South Africa, is the southernmost country in Africa. South Africa is the 25th-largest country in the world by land area and it is the southernmost country on the mainland of the Old World or the Eastern Hemisphere. About 80 percent of South Africans are of Sub-Saharan African ancestry, divided among a variety of ethnic groups speaking different Bantu languages, the remaining population consists of Africas largest communities of European, Asian, and multiracial ancestry. South Africa is a multiethnic society encompassing a variety of cultures, languages. Its pluralistic makeup is reflected in the recognition of 11 official languages. The country is one of the few in Africa never to have had a coup détat, however, the vast majority of black South Africans were not enfranchised until 1994. During the 20th century, the black majority sought to recover its rights from the dominant white minority, with this struggle playing a role in the countrys recent history. The National Party imposed apartheid in 1948, institutionalising previous racial segregation, since 1994, all ethnic and linguistic groups have held political representation in the countrys democracy, which comprises a parliamentary republic and nine provinces. South Africa is often referred to as the Rainbow Nation to describe the multicultural diversity. The World Bank classifies South Africa as an economy. Its economy is the second-largest in Africa, and the 34th-largest in the world, in terms of purchasing power parity, South Africa has the seventh-highest per capita income in Africa. However, poverty and inequality remain widespread, with about a quarter of the population unemployed, nevertheless, South Africa has been identified as a middle power in international affairs, and maintains significant regional influence. The name South Africa is derived from the geographic location at the southern tip of Africa. Upon formation the country was named the Union of South Africa in English, since 1961 the long form name in English has been the Republic of South Africa. In Dutch the country was named Republiek van Zuid-Afrika, replaced in 1983 by the Afrikaans Republiek van Suid-Afrika, since 1994 the Republic has had an official name in each of its 11 official languages. Mzansi, derived from the Xhosa noun umzantsi meaning south, is a name for South Africa. South Africa contains some of the oldest archaeological and human fossil sites in the world, extensive fossil remains have been recovered from a series of caves in Gauteng Province. The area is a UNESCO World Heritage site and has termed the Cradle of Humankind
South Africa
–
Mapungubwe Hill, the site of the former capital of the
Kingdom of Mapungubwe
South Africa
–
Flag
South Africa
–
Arrival of
Jan van Riebeeck, the first European to settle in South Africa, with
Devil's Peak in the background
South Africa
–
Depiction of a
Zulu attack on a Boer camp in February 1838
