1.
Sedimentary
–
Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the Earths surface and within bodies of water. Sedimentation is the name for processes that cause mineral and/or organic particles to settle in place. The particles that form a rock by accumulating are called sediment. Sedimentation may also occur as minerals precipitate from solution or shells of aquatic creatures settle out of suspension. The sedimentary rock cover of the continents of the Earths crust is extensive, sedimentary rocks are only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks. Sedimentary rocks are deposited in layers as strata, forming a structure called bedding, sedimentary rocks are also important sources of natural resources like coal, fossil fuels, drinking water or ores. The study of the sequence of rock strata is the main source for an understanding of the Earths history, including palaeogeography, paleoclimatology. The scientific discipline that studies the properties and origin of rocks is called sedimentology. Sedimentology is part of both geology and physical geography and overlaps partly with other disciplines in the Earth sciences, such as pedology, geomorphology, geochemistry, sedimentary rocks have also been found on Mars. Clastic sedimentary rocks are composed of rock fragments that were cemented by silicate minerals. Clastic rocks are composed largely of quartz, feldspar, rock fragments, clay minerals, and mica, any type of mineral may be present, clastic sedimentary rocks, are subdivided according to the dominant particle size. Most geologists use the Udden-Wentworth grain size scale and divide unconsolidated sediment into three fractions, gravel, sand, and mud and this tripartite subdivision is mirrored by the broad categories of rudites, arenites, and lutites, respectively, in older literature. The subdivision of these three categories is based on differences in clast shape, conglomerates and breccias), composition. Conglomerates are dominantly composed of rounded gravel, while breccias are composed of dominantly angular gravel, composition of framework grains The relative abundance of sand-sized framework grains determines the first word in a sandstone name. Naming depends on the dominance of the three most abundant components quartz, feldspar, or the lithic fragments that originated from other rocks, all other minerals are considered accessories and not used in the naming of the rock, regardless of abundance. Clean sandstones with open space are called arenites. Muddy sandstones with abundant muddy matrix are called wackes, six sandstone names are possible using the descriptors for grain composition and the amount of matrix. Mudrocks are sedimentary rocks composed of at least 50% silt- and clay-sized particles and these relatively fine-grained particles are commonly transported by turbulent flow in water or air, and deposited as the flow calms and the particles settle out of suspension
Sedimentary
–
Middle
Triassic marginal marine sequence of siltstones (reddish layers at the cliff base) and limestones (brown rocks above),
Virgin Formation, southwestern
Utah, USA
Sedimentary
–
Sedimentary rocks on Mars, investigated by NASA's
Curiosity Mars rover
Sedimentary
–
Steeply dipping sedimentary rock strata along the
Chalous Road in northern
Iran
Sedimentary
–
Claystone deposited in
Glacial Lake Missoula,
Montana,
United States. Note the very fine and flat bedding, common for distal
lacustrine deposition.
2.
Liesegang rings (geology)
–
Liesegang rings are colored bands of cement observed in sedimentary rocks that typically cut-across bedding. These secondary sedimentary structures exhibit bands of minerals that are arranged in a repeating pattern. Liesegang rings are distinguishable from other structures by their concentric or ring-like appearance. The resultant precipitate of silver dichromate formed a pattern of rings. Liesegang and successive other workers observed the behavior of precipitates forming rings in sedimentary rocks, the process by which Liesegang rings develop is not completely understood. Liesegang rings may form from the segregation of iron oxides. In this process the. diffusion of reactants leads to supersaturation and nucleation, one classic example based on the Ostwald-Liesegang hypothesis is observed in water and rock interactions where iron hydroxide precipitates in sandstone through pore space. Liesegang ring patterns are considered to be secondary sedimentary structures, though they are found in permeable igneous. Chemical weathering of rocks that leads to the formation of Liesegang rings typically involves the diffusion of oxygen in water into pore space containing soluble ferrous iron. Liesegang rings usually cut across layers of stratification and occur in many types of rock, some of more commonly include sandstone. Though there is an occurrence of Liesegang rings in sedimentary rocks, relatively few scientists have studied their mineralogy. Pseudofaults are the result of Liesegang rings developing within areas of the rock that are adjacent to each other but at varying stratigraphic levels
Liesegang rings (geology)
–
Typical Liesegang ring structures within cross-section
Liesegang rings (geology)
–
Anvil rock, Shawnee National Forest, IL
Liesegang rings (geology)
–
The bridge with the ring visible in the lower left quadrant.
Liesegang rings (geology)
–
A close view of the ring shown above.
3.
Quartz
–
Quartz is the second most abundant mineral in Earths continental crust, behind feldspar. There are many different varieties of quartz, several of which are semi-precious gemstones, since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Eurasia. The word quartz is derived from the German word Quarz and its Middle High German ancestor twarc, the Ancient Greeks referred to quartz as κρύσταλλος derived from the Ancient Greek κρύος meaning icy cold, because some philosophers apparently believed the mineral to be a form of supercooled ice. Today, the rock crystal is sometimes used as an alternative name for the purest form of quartz. Quartz belongs to the crystal system. The ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end, well-formed crystals typically form in a bed that has unconstrained growth into a void, usually the crystals are attached at the other end to a matrix and only one termination pyramid is present. However, doubly terminated crystals do occur where they develop freely without attachment, a quartz geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward. α-quartz crystallizes in the crystal system, space group P3121 and P3221 respectively. β-quartz belongs to the system, space group P6222 and P6422. These space groups are truly chiral, both α-quartz and β-quartz are examples of chiral crystal structures composed of achiral building blocks. The transformation between α- and β-quartz only involves a comparatively minor rotation of the tetrahedra with respect to one another, although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is an identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent, common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others. The most important distinction between types of quartz is that of macrocrystalline and the microcrystalline or cryptocrystalline varieties, the cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony is a form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite. Other opaque gemstone varieties of quartz, or mixed rocks including quartz, often including contrasting bands or patterns of color, are agate, carnelian or sard, onyx, heliotrope, amethyst is a form of quartz that ranges from a bright to dark or dull purple color. The worlds largest deposits of amethysts can be found in Brazil, Mexico, Uruguay, Russia, France, Namibia, sometimes amethyst and citrine are found growing in the same crystal. It is then referred to as ametrine, an amethyst is formed when there is iron in the area where it was formed
Quartz
–
Quartz
crystal cluster from
Tibet
Quartz
–
Clear rock crystals on a white base
Quartz
–
Amethyst crystals on matrix
Quartz
–
Citrine from Brazil
4.
Feldspar
–
Feldspars are a group of rock-forming tectosilicate minerals that make up about 40% of the Earths continental crust. Feldspars crystallize from magma as veins in both intrusive and extrusive rocks and are also present in many types of metamorphic rock. Rock formed almost entirely of plagioclase feldspar is known as anorthosite. Feldspars are also found in types of sedimentary rocks. The name feldspar derives from the German Feldspat, a compound of the words Feld, field, and Spat, the change from Spat to -spar was influenced by the English word spar, a synonym for mineral. Feldspathic refers to materials that contain feldspar, the alternate spelling, felspar, has largely fallen out of use. This group of minerals consists of tectosilicates, solid solutions between albite and anorthite are called plagioclase, or more properly plagioclase feldspar. Only limited solid solution occurs between K-feldspar and anorthite, and in the two solid solutions, immiscibility occurs at temperatures common in the crust of the earth. Albite is considered both a plagioclase and alkali feldspar, the alkali feldspars are as follows, orthoclase —KAlSi3O8 sanidine —AlSi3O8 microcline —KAlSi3O8 anorthoclase —AlSi3O8 Sanidine is stable at the highest temperatures, and microcline at the lowest. Perthite is a texture in alkali feldspar, due to exsolution of contrasting alkali feldspar compositions during cooling of an intermediate composition. The perthitic textures in the alkali feldspars of many granites can be seen with the naked eye, microperthitic textures in crystals are visible using a light microscope, whereas cryptoperthitic textures can be seen only with an electron microscope. Barium feldspars are also considered alkali feldspars, barium feldspars form as the result of the substitution of barium for potassium in the mineral structure. The barium feldspars are monoclinic and include the following, celsian—BaAl2Si2O8 hyalophane—4O8 The plagioclase feldspars are triclinic, the immiscibility gaps in the plagioclase solid solutions are complex compared to the gap in the alkali feldspars. The play of colours visible in some feldspar of labradorite composition is due to very fine-grained exsolution lamellae, chemical weathering of feldspars results in the formation of clay minerals. About 20 million tonnes of feldspar were produced in 2010, mostly by three countries, Italy, Turkey, and China, Feldspar is a common raw material used in glassmaking, ceramics, and to some extent as a filler and extender in paint, plastics, and rubber. In glassmaking, alumina from feldspar improves product hardness, durability, in ceramics, the alkalis in feldspar act as a flux, lowering the melting temperature of a mixture. Fluxes melt at a stage in the firing process, forming a glassy matrix that bonds the other components of the system together. In the US, about 66% of feldspar is consumed in glassmaking, including glass containers, ceramics and other uses, such as fillers, accounted for the remainder
Feldspar
–
Feldspar crystal (18×21×8.5 cm) from
Jequitinhonha valley,
Minas Gerais, Southeastern Brazil.
Feldspar
–
Compositional phase diagram of the different minerals that constitute the feldspar solid solution.
Feldspar
–
Lunar ferrous
anorthosite #60025 (
plagioclase feldspar). Collected by
Apollo 16 from the
Lunar Highlands near
Descartes Crater. This sample is currently on display at the
National Museum of Natural History in
Washington, D.C.
Feldspar
–
Labradorite.
5.
Lithic fragment (geology)
–
Lithic fragments, or lithics, are pieces of other rocks that have been eroded down to sand size and now are sand grains in a sedimentary rock. They were first described and named by Bill Dickinson in 1970, lithic fragments can be derived from sedimentary, igneous or metamorphic rocks). A lithic fragment is defined using the Gazzi-Dickinson point-counting method and being in the sand-size fraction, sand grains in sedimentary rocks that are fragments of larger rocks that are not identified using the Gazzi-Dickinson method are usually called rock fragments instead of lithic fragments. Sandstones rich in lithic fragments are called lithic sandstones and these can include granular, microlitic, lathwork, and vitric. These correlations between composition and volcanic lithic fragment type are approximate, at best, by definition, intrusive igneous rock fragments can not be considered lithic fragments. These can include shale siltstone fragments, and chert and these can include fine-grained schist and phyllite fragments, among others
Lithic fragment (geology)
–
Granular volcanic lithic fragment, scale in
millimeters Top picture in plane-
polarized light, bottom picture in cross-polarized light.
Lithic fragment (geology)
–
Microlitic volcanic lithic fragment, scale in millimeters. Top picture in plane-polarized light, bottom picture in cross-polarized light.
Lithic fragment (geology)
–
Lathwork volcanic lithic fragment, scale in millimeters. Top picture in plane-polarized light, bottom picture in cross-polarized light.
6.
Devonian
–
The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian,419.2 million years ago, to the beginning of the Carboniferous,358.9 Mya. It is named after Devon, England, where rocks from this period were first studied, the first significant adaptive radiation of life on dry land occurred during the Devonian. Free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents, by the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods also became well-established, Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the Age of Fish. The first ray-finned and lobe-finned bony fish appeared, while the placodermi began dominating almost every aquatic environment. The ancestors of all four-limbed vertebrates began adapting to walking on land, as their strong pectoral, in the oceans, primitive sharks became more numerous than in the Silurian and Late Ordovician. The first ammonites, species of molluscs, appeared, trilobites, the mollusk-like brachiopods and the great coral reefs, were still common. The Late Devonian extinction which started about 375 million years ago severely affected marine life, killing off all placodermi, and all trilobites, save for a few species of the order Proetida. The palaeogeography was dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, while the rock beds that define the start and end of the Devonian period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy, the Devonian extends from the end of the Silurian 419.2 Mya, another common term is Age of the Fishes, referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into the Downtonian, Dittonian, Breconian and Farlovian stages, in the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common. The Devonian Period is formally broken into Early, Middle and Late subdivisions, the rocks corresponding to those epochs are referred to as belonging to the Lower, Middle and Upper parts of the Devonian System. Early Devonian The Early Devonian lasted from 419.2 ±2.8 to 393.3 ±2.5 and began with the Lochkovian stage, which lasted until the Pragian. It spanned from 410.8 ±2.8 to 407.6 ±2.5, and was followed by the Emsian, which lasted until the Middle Devonian began,393. 3±2.7 million years ago. Middle Devonian The Middle Devonian comprised two subdivisions, first the Eifelian, which gave way to the Givetian 387. 7±2.7 million years ago. Late Devonian Finally, the Late Devonian started with the Frasnian,382.7 ±2.8 to 372.2 ±2.5, during which the first forests took shape on land. The first tetrapods appeared in the record in the ensuing Famennian subdivision. This lasted until the end of the Devonian,358. 9±2.5 million years ago, the Devonian was a relatively warm period, and probably lacked any glaciers
Devonian
–
The rocks of Lummaton Quarry in
Torquay in Devon played an early role in defining the Devonian period.
Devonian
–
Dunkleosteus, one of the largest armoured fish to ever roam the planet, lived during the late Devonian
Devonian
–
Enrolled phacopid
trilobite from the Devonian of Ohio
Devonian
–
The common tabulate coral
Aulopora from the Middle Devonian of Ohio – view of colony origin encrusting a
brachiopod valve
7.
Estonia
–
Estonia, officially the Republic of Estonia, is a country in the Baltic region of Northern Europe. It is bordered to the north by the Gulf of Finland, to the west by the Baltic Sea, to the south by Latvia, across the Baltic Sea lies Sweden in the west and Finland in the north. The territory of Estonia consists of a mainland and 2,222 islands and islets in the Baltic Sea, covering 45,339 km2 of land and water, and is influenced by a humid continental climate. The territory of Estonia has been inhabited since at least 6500 BC, in 1988, during the Singing Revolution, the Estonian Supreme Soviet issued the Estonian Sovereignty Declaration in defiance of Soviet rule, and independence was restored on 20 August 1991. Estonia is a parliamentary republic divided into fifteen counties. Its capital and largest city is Tallinn, with a population of 1.3 million, it is one of the least-populous member states of the European Union, Eurozone, North Atlantic Treaty Organization, OECD and Schengen Area. Estonia is a country with an advanced, high-income economy that is among the fastest growing in the EU. Its Human Development Index ranks very highly, and it performs favourably in measurements of economic freedom, civil liberties, the 2015 PISA test places Estonian high school students 3rd in the world, behind Singapore and Japan. Citizens of Estonia are provided with health care, free education. Since independence the country has developed its IT sector, becoming one of the worlds most digitally advanced societies. In 2005 Estonia became the first nation to hold elections over the Internet, in the Estonian language, the oldest known endonym of the Estonians was maarahvas, meaning country people or people of the land. The land inhabited by Estonians was called Maavald meaning Country Parish or Land Parish, one hypothesis regarding the modern name of Estonia is that it originated from the Aesti, a people described by the Roman historian Tacitus in his Germania. The historic Aesti were allegedly Baltic people, whereas the modern Estonians are Finno-Ugric, the geographical areas between Aesti and Estonia do not match, with Aesti being further down south. Ancient Scandinavian sagas refer to a land called Eistland, as the country is called in Icelandic. Early Latin and other ancient versions of the name are Estia and Hestia, esthonia was a common alternative English spelling prior to 1921. Human settlement in Estonia became possible 13,000 to 11,000 years ago, the oldest known settlement in Estonia is the Pulli settlement, which was on the banks of the river Pärnu, near the town of Sindi, in south-western Estonia. According to radiocarbon dating it was settled around 11,000 years ago, the earliest human inhabitation during the Mesolithic period is connected to Kunda culture, which is named after the town of Kunda in northern Estonia. At that time the country was covered with forests, and people lived in communities near bodies of water
Estonia
–
Tools made by Kunda culture,
Estonian History Museum
Estonia
Estonia
–
Iron Age artifacts of a hoard from
Kumna
Estonia
–
A stylised
viking ship on the Estonian 1
Kroon from 1934
8.
Navajo Sandstone
–
Navajo Sandstone frequently overlies and interfingers with the Kayenta Formation of the Glen Canyon Group. Together, these formations can result in immense vertical cliffs of up to 2,200 feet, atop the cliffs, Navajo Sandstone often appears as massive rounded domes and bluffs that are generally white in color. Navajo Sandstone frequently occurs as spectacular cliffs, cuestas, domes and it can be distinguished from adjacent Jurassic sandstones by its white to light pink color, meter-scale cross-bedding, and distinctive rounded weathering. The wide range of colors exhibited by the Navajo Sandstone reflect a history of alteration by groundwater and other subsurface fluids over the last 190 million years. The iron in these strata originally arrived via the erosion of iron-bearing silicate minerals, initially, this iron accumulated as iron-oxide coatings, which formed slowly after the sand had been deposited. Later, after having been buried, reducing fluids composed of water. The dissolution of the iron coatings by the reducing fluids bleached large volumes of the Navajo Sandstone a brilliant white, reducing fluids transported the iron in solution until they mixed with oxidizing groundwater. Where the oxidizing and reducing fluids mixed, the iron precipitated within the Navajo Sandstone, the precipitation of iron oxides also formed laminea, corrugated layers, columns, and pipes of ironstone within the Navajo Sandstone. The age of the Navajo Sandstone is somewhat controversial and it may originate from the Late Triassic but is at least as young as the Early Jurassic stages Pliensbachian and Toarcian. There is no type locality of the name and it was simply named for the Navajo Country of the southwestern United States. The two major subunits of the Navajo are the Lamb Point Tongue and the Shurtz Sandstone Tongue, the Navajo Sandstone was originally named as the uppermost formation of the La Plata Group by Gregory and Stone in 1917. Baker reassigned it as the formation of Glen Canyon Group in 1936. Its age was modified by Lewis and others in 1961, the name was originally not used in northwest Colorado and northeast Utah, where the name Glen Canyon Sandstone was preferred. Its age was modified again by Padian in 1989, the sandstone was deposited in an arid erg on the Western portion of the Supercontinent Pangaea. This region was affected by monsoons that came about each winter when cooler winds. Theropod tracks are located in Arizona, Colorado, and Utah. Ornithischian tracks located in Arizona, USA, the Navajo Sandstone is also well known among rockhounds for its hundreds of thousands of iron oxide concretions. They are believed to represent an extension of Hopi Native American traditions regarding ancestor worship, informally, they are called Moqui marbles after the local proposed Moqui Native American tribe
Navajo Sandstone
–
A prominent
cuesta of Navajo Sandstone rims the edge of the San Rafael Swell in eastern Utah.
Navajo Sandstone
–
Alcove near
Moab, Utah.
Navajo Sandstone
–
Stevens Arch, near the mouth of
Coyote Gulch in the
Canyons of the Escalante, is formed from a layer of Navajo Sandstone. The opening is 220 feet (67 m) wide and 160 feet (49 m) high.
Navajo Sandstone
9.
Petra
–
Petra, originally known to the Nabataeans as Raqmu, is a historical and archaeological city in southern Jordan. The city is famous for its architecture and water conduit system. Another name for Petra is the Rose City due to the color of the out of which it is carved. Established possibly as early as 312 BC as the city of the Arab Nabataeans, it is a symbol of Jordan. The Nabataeans were nomadic Arabs who took advantage of Petras proximity to trade routes to establish it as a major trading hub. The Nabataeans are also known for their ability in constructing efficient water-collecting methods in the barren deserts. Petra lies on the slope of Jebel al-Madhbah in a basin among the mountains form the eastern flank of Arabah. It has been a UNESCO World Heritage Site since 1985, the site remained unknown to the western world until 1812, when it was introduced by Swiss explorer Johann Ludwig Burckhardt. It was described as a rose-red city half as old as time in a Newdigate Prize-winning poem by John William Burgon, UNESCO has described it as one of the most precious cultural properties of mans cultural heritage. Petra was named amongst the New7Wonders of the World in 2007 and was chosen by the Smithsonian Magazine as one of the 28 Places to See Before You Die. Pliny the Elder and other writers identify Petra as the capital of the Nabataeans, excavations have demonstrated that it was the ability of the Nabataeans to control the water supply that led to the rise of the desert city, creating an artificial oasis. The area is visited by flash floods, and archaeological evidence demonstrates the Nabataeans controlled these floods by the use of dams, cisterns and these innovations stored water for prolonged periods of drought and enabled the city to prosper from its sale. Another approach was possibly from the plateau to the north. Today, most modern visitors approach the site from the east, at the end of the narrow gorge stands Petras most elaborate ruin, Al Khazneh, hewn into the sandstone cliff. A little farther from the Treasury, at the foot of the mountain called en-Nejr, is a massive theatre, at the point where the valley opens out into the plain, the site of the city is revealed with striking effect. The amphitheatre has been cut into the hillside and into several of the tombs during its construction, rectangular gaps in the seating are still visible. Almost enclosing it on three sides are rose-colored mountain walls, divided into groups by deep fissures and lined with knobs cut from the rock in the form of towers. By 2010 BC, some of the earliest recorded farmers had settled in Beidha, Petra is listed in Egyptian campaign accounts and the Amarna letters as Pel, Sela or Seir
Petra
–
Al Khazneh or The Treasury at Petra
Petra
–
The narrow passage (
Siq) that leads to Petra
Petra
–
Petra at night
Petra
–
One of the many tombs in Petra
10.
Clastic sedimentary rock
–
Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus, chunks and smaller grains of rock broken off other rocks by physical weathering. Geologists use the term clastic with reference to sedimentary rocks as well as to particles in sediment transport whether in suspension or as bed load, clastic sedimentary rocks are rocks composed predominantly of broken pieces or clasts of older weathered and eroded rocks. Clastic sediments or sedimentary rocks are classified based on size, clast and cementing material composition. The classification factors are often useful in determining a samples environment of deposition, an example clastic environment would be a river system in which the full range of grains being transported by the moving water consist of pieces eroded from solid rock upstream. Grain size varies from clay in shales and claystones, through silt in siltstones, sand in sandstones, the Krumbein phi scale numerically orders these terms in a logarithmic size scale. Siliciclastic rocks are clastic rocks that are composed almost exclusively of silicon. The composition of sedimentary rocks includes the chemical and mineralogical components of the framework as well as the cementing material that make up these rocks. Boggs divides them into four categories, major minerals, accessory minerals, rock fragments, major minerals can be categorized into subdivisions based on their resistance to chemical decomposition. Those that possess a great resistance to decomposition are categorized as stable, while those that do not are considered less stable, the most common stable mineral in siliciclastic sedimentary rocks is quartz. Quartz makes up approximately 65 percent of framework grains present in sandstones, less stable minerals present in this type of rocks are feldspars, including both potassium and plagioclase feldspars. Feldspars comprise a considerably lesser portion of framework grains and minerals and they only make up about 15 percent of framework grains in sandstones and 5% of minerals in shales. Clay mineral groups are present in mudrocks but can be found in other siliciclastic sedimentary rocks at considerably lower levels. Accessory minerals are associated with those whose presence in the rock are not directly important to the classification of the specimen and these generally occur in smaller amounts in comparison to the quartz, and feldspars. Furthermore, those that do occur are generally heavy minerals or coarse grained micas, rock fragments also occur in the composition of siliciclastic sedimentary rocks and are responsible for about 10 -15 percent of the composition of sandstone. They generally make up most of the gravel size particles in conglomerates, though they sometimes are, rock fragments are not always sedimentary in origin. They can also be metamorphic or igneous, chemical cements vary in abundance but are predominantly found in sandstones. The two major types, are based and carbonate based
Clastic sedimentary rock
–
Middle
Triassic marginal marine sequence of siltstones (reddish layers at the cliff base) and limestones (brown rocks above),
Virgin Formation, southwestern
Utah, USA
Clastic sedimentary rock
–
Sedimentary rocks on Mars, investigated by NASA's
Curiosity Mars rover
Clastic sedimentary rock
–
Steeply dipping sedimentary rock strata along the
Chalous Road in northern
Iran
Clastic sedimentary rock
–
Claystone deposited in
Glacial Lake Missoula,
Montana,
United States. Note the very fine and flat bedding, common for distal
lacustrine deposition.
11.
Grain size
–
Particle size, also called grain size, refers to the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials and this is different from the crystallite size, which refers to the size of a single crystal inside a particle or grain. A single grain can be composed of several crystals, granular material can range from very small colloidal particles, through clay, silt, sand, gravel, and cobbles, to boulders. Size ranges define limits of classes that are given names in the Wentworth scale used in the United States, the Krumbein phi scale, a modification of the Wentworth scale created by W. C. This equation can be rearranged to find diameter using φ, D = D0 ×2 − ϕ In some schemes, ISO 14688-1 is applicable to natural soils in situ, similar man-made materials in situ and soils redeposited by people. An accumulation of sediment can also be characterized by the size distribution. A sediment deposit can undergo sorting when a particle size range is removed by an agency such as a river or the wind, a Scale of Grade and Class Terms for Clastic Sediments
Grain size
–
Wentworth grain size chart from United States Geological Survey Open-File Report 2006-1195
Grain size
–
Beach cobbles (gravel) at Nash Point, South Wales.
Grain size
12.
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.
13.
Weathering
–
Weathering is the breaking down of rocks, soil, and minerals as well as wood and artificial materials through contact with the Earths atmosphere, waters, and biological organisms. Two important classifications of weathering processes exist – physical and chemical weathering, mechanical or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure. While physical weathering is accentuated in very cold or very dry environments, chemical reactions are most intense where the climate is wet, however, both types of weathering occur together, and each tends to accelerate the other. For example, physical abrasion decreases the size of particles and therefore increases their surface area, the various agents act in concert to convert primary minerals to secondary minerals and release plant nutrient elements in soluble forms. The materials left over after the rock breaks down combined with organic material creates soil, in addition, many of Earths landforms and landscapes are the result of weathering processes combined with erosion and re-deposition. Physical weathering, also recognized as mechanical weathering, is the class of processes that causes the disintegration of rocks without chemical change, the primary process in physical weathering is abrasion. However, chemical and physical weathering often go hand in hand, physical weathering can occur due to temperature, pressure, frost etc. For example, cracks exploited by physical weathering will increase the area exposed to chemical action. Abrasion by water, ice, and wind loaded with sediment can have tremendous cutting power, as is amply demonstrated by the gorges, ravines. In glacial areas, huge moving ice masses embedded with soil and rock fragments grind down rocks in their path, plant roots sometimes enter cracks in rocks and pry them apart, resulting in some disintegration, Burrowing animals may help disintegrate rock through their physical action. However, such influences are usually of importance in producing parent material when compared to the drastic physical effects of water, ice, wind. Physical weathering is called mechanical weathering or disaggregation. Thermal stress weathering results from the expansion and contraction of rock, for example, heating of rocks by sunlight or fires can cause expansion of their constituent minerals. As some minerals expand more than others, temperature changes set up differential stresses that cause the rock to crack apart. Because the outer surface of a rock is often warmer or colder than the more protected inner portions and this process may be sharply accelerated if ice forms in the surface cracks. When water freezes, it expands with a force of about 1465 Mg/m^2, disintegrating huge rock masses, thermal stress weathering comprises two main types, thermal shock and thermal fatigue. Thermal stress weathering is an important mechanism in deserts, where there is a diurnal temperature range, hot in the day. The repeated heating and cooling exerts stress on the layers of rocks
Weathering
–
A
natural arch produced by erosion of differentially weathered rock in Jebel Kharaz (
Jordan)
Weathering
–
A rock in
Abisko,
Sweden fractured along existing
joints possibly by frost weathering or thermal stress
Weathering
–
Wave action and water chemistry lead to structural failure in exposed rocks
Weathering
–
Pressure release could have caused the exfoliated granite sheets shown in the picture.
14.
Sand
–
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. It is defined by size, being finer than gravel and coarser than silt, Sand can also refer to a textural class of soil or soil type, i. e. a soil containing more than 85% sand-sized particles by mass. The second most common type of sand is calcium carbonate, for example aragonite, for example, it is the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years like the Caribbean. Sand is a non renewable resource over human timescales, and sand suitable for making concrete is in high demand, in terms of particle size as used by geologists, sand particles range in diameter from 0.0625 mm to 2 mm. An individual particle in this size is termed a sand grain. Sand grains are between gravel and silt, a 1953 engineering standard published by the American Association of State Highway and Transportation Officials set the minimum sand size at 0.074 mm. A1938 specification of the United States Department of Agriculture was 0.05 mm. Sand feels gritty when rubbed between the fingers. ISO14688 grades sands as fine, medium and coarse with ranges 0.063 mm to 0.2 mm to 0.63 mm to 2.0 mm. In the United States, sand is commonly divided into five sub-categories based on size, very fine sand, fine sand, medium sand, coarse sand, and very coarse sand. These sizes are based on the Krumbein phi scale, where size in Φ = -log2D, on this scale, for sand the value of Φ varies from −1 to +4, with the divisions between sub-categories at whole numbers. The composition of sand is highly variable, depending on the local rock sources. The gypsum sand dunes of the White Sands National Monument in New Mexico are famous for their bright, arkose is a sand or sandstone with considerable feldspar content, derived from weathering and erosion of a granitic rock outcrop. Some sands contain magnetite, chlorite, glauconite or gypsum, Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts and obsidian. Chlorite-glauconite bearing sands are typically green in color, as are sands derived from basaltic with a high olivine content, many sands, especially those found extensively in Southern Europe, have iron impurities within the quartz crystals of the sand, giving a deep yellow color. Sand deposits in some areas contain garnets and other resistant minerals, the study of individual grains can reveal much historical information as to the origin and kind of transport of the grain. Quartz sand that is weathered from granite or gneiss quartz crystals will be angular. It is called grus in geology or sharp sand in the trade where it is preferred for concrete. Sand that is transported long distances by water or wind will be rounded, people who collect sand as a hobby are known as arenophiles
Sand
–
Sand
dunes in the
Idehan Ubari, Libya.
Sand
–
Close-up (1×1 cm) of sand from the
Gobi Desert, Mongolia.
Sand
–
Heavy minerals (dark) in a quartz beach sand (
Chennai, India).
Sand
–
Sand from
Coral Pink Sand Dunes State Park,
Utah. These are grains of
quartz with a
hematite coating providing the orange color.
15.
Topography
–
Topography is the study of the shape and features of the surface of the Earth and other observable astronomical objects including planets, moons, and asteroids. The topography of an area could refer to the shapes and features themselves. This field of geoscience and planetary science is concerned with detail in general, including not only relief but also natural and artificial features. This meaning is common in the United States, where topographic maps with elevation contours have made topography synonymous with relief. The older sense of topography as the study of place still has currency in Europe, topography in a narrow sense involves the recording of relief or terrain, the three-dimensional quality of the surface, and the identification of specific landforms. This is also known as geomorphometry, in modern usage, this involves generation of elevation data in digital form. It is often considered to include the representation of the landform on a map by a variety of techniques, including contour lines, hypsometric tints. The term topography originated in ancient Greece and continued in ancient Rome, the word comes from the Greek τόπος and -γραφία. In classical literature this refers to writing about a place or places, in Britain and in Europe in general, the word topography is still sometimes used in its original sense. Detailed military surveys in Britain were called Ordnance Surveys, and this term was used into the 20th century as generic for topographic surveys, the earliest scientific surveys in France were called the Cassini maps after the family who produced them over four generations. The term topographic surveys appears to be American in origin, the earliest detailed surveys in the United States were made by the “Topographical Bureau of the Army, ” formed during the War of 1812, which became the Corps of Topographical Engineers in 1838. In the 20th century, the term started to be used to describe surface description in other fields where mapping in a broader sense is used. An objective of topography is to determine the position of any feature or more generally any point in terms of both a horizontal coordinate system such as latitude, longitude, and altitude, identifying features, and recognizing typical landform patterns are also part of the field. There are a variety of approaches to studying topography, which method to use depend on the scale and size of the area under study, its accessibility, and the quality of existing surveys. Work on one of the first topographic maps was begun in France by Giovanni Domenico Cassini, in areas where there has been an extensive direct survey and mapping program, the compiled data forms the basis of basic digital elevation datasets such as USGS DEM data. This data must often be cleaned to eliminate discrepancies between surveys, but it forms a valuable set of information for large-scale analysis. The original American topographic surveys involved not only recording of relief, remote sensing is a general term for geodata collection at a distance from the subject area. Besides their role in photogrammetry, aerial and satellite imagery can be used to identify and delineate terrain features, certainly they have become more and more a part of geovisualization, whether maps or GIS systems
Topography
–
A surveying point in
Germany
Topography
–
A topographic map with
contour intervals
16.
Percolation
–
In physics, chemistry and materials science, percolation refers to the movement and filtering of fluids through porous materials. For example, in geology, percolation refers to filtration of water through soil, the water flows to recharge the groundwater in the water table and aquifers. Statistical physics concepts such as scaling theory, renormalization, phase transition, critical phenomena, combinatorics is commonly employed to study percolation thresholds. Due to the complexity involved in obtaining exact results from analytical models of percolation, the current fastest algorithm for percolation was published in 2000 by Mark Newman and Robert Ziff. Example/theory, A hole is dug in the ground surface, water is filled in to the hole and the time is measured for a drop of one inch in the water surface. If the water surface quickly drops, as seen in poorly-graded sands. If the hydraulic conductivity of the site is low then the site is undesirable, notices of the AMS, May 2006. ISBN 0-7484-0075-3, ISBN 0-7484-0076-1 Geoffrey Grimmett, introduction to Percolation Theory A. Bunde, S. Havlin Fractals and Disordered Systems, Springer,1996 S. Kirkpatrick Percolation and conduction Rev. Mod
Percolation
–
In coffee percolation, soluble compounds leave the coffee grounds and join the water to form
coffee. Insoluble compounds remain within the
coffee filter.
17.
Porosity
–
Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0 and 100%. Strictly speaking, some measure the accessible void, the total amount of void space accessible from the surface. There are many ways to test porosity in a substance or part, the term porosity is used in multiple fields including pharmaceutics, ceramics, metallurgy, materials, manufacturing, earth sciences, soil mechanics and engineering. Void fraction usually varies from location to location in the flow channel and it fluctuates with time and its value is usually time averaged. In separated flow, it is related to flow rates of the gas and the liquid phase. It is defined by the ratio, ϕ = V V V T where VV is the volume of void-space and VT is the total or bulk volume of material, both the mathematical symbols ϕ and n are used to denote porosity. Porosity is a fraction between 0 and 1, typically ranging from less than 0.01 for solid granite to more than 0.5 for peat and it may also be represented in percent terms by multiplying the fraction by 100. The porosity of a rock, or sedimentary layer, is an important consideration when attempting to evaluate the potential volume of water or hydrocarbons it may contain. Sedimentary porosity is a function of many factors, including but not limited to, rate of burial, depth of burial, the nature of the connate fluids. The principal complication is that there is not a direct proportionality between porosity and hydraulic conductivity but rather an inferred proportionality, there is a clear proportionality between pore throat radii and hydraulic conductivity. Also, there tends to be a proportionality between pore throat radii and pore volume, if the proportionality between pore throat radii and porosity exists then a proportionality between porosity and hydraulic conductivity may exist. Well sorted materials have higher porosity than similarly sized poorly sorted materials, for tables of common porosity values for earth materials, see the further reading section in the Hydrogeology article. Consolidated rocks potentially have more complex dual porosities, as compared with alluvial sediment and this can be split into connected and unconnected porosity. Connected porosity is more easily measured through the volume of gas or liquid that can flow into the rock, porosity is the ratio of pore volume to its total volume. Porosity is controlled by, rock type, pore distribution, cementation, diagenetic history, porosity is not controlled by grain size, as the volume of between-grain space is related only to the method of grain packing. Rocks normally decrease in porosity with age and depth of burial, tertiary age Gulf Coast sandstones are in general more porous than Cambrian age sandstones. There are exceptions to this rule, usually because of the depth of burial and thermal history, porosity of surface soil typically decreases as particle size increases. This is due to soil formation in finer textured surface soils when subject to soil biological processes
Porosity
–
Optical method of measuring porosity:
thin section under gypsum plate shows porosity as purple color, contrasted with carbonate grains of other colors.
Pleistocene eolianite from
San Salvador Island, Bahamas. Scale bar 500
µm.
Porosity
–
Effects of sorting on
alluvial porosity
18.
Aquifer
–
An aquifer is an underground layer of water-bearing permeable rock, rock fractures or unconsolidated materials from which groundwater can be extracted using a water well. The study of flow in aquifers and the characterization of aquifers is called hydrogeology. Related terms include aquitard, which is a bed of low permeability along an aquifer, and aquiclude, if the impermeable area overlies the aquifer, pressure could cause it to become a confined aquifer. Aquifers may occur at various depths and those closer to the surface are not only more likely to be used for water supply and irrigation, but are also more likely to be topped up by the local rainfall. Many desert areas have limestone hills or mountains within them or close to them that can be exploited as groundwater resources, overexploitation can lead to the exceeding of the practical sustained yield, i. e. more water is taken out than can be replenished. The beach provides a model to help visualize an aquifer, if a hole is dug into the sand, very wet or saturated sand will be located at a shallow depth. This hole is a well, the wet sand represents an aquifer. In 2013 large freshwater aquifers were discovered under continental shelves off Australia, China, North America and they contain an estimated half a million cubic kilometers of “low salinity” water that could be economically processed into potable water. The reserves formed when ocean levels were lower and rainwater made its way into the ground in areas that were not submerged until the ice age ended 20,000 years ago. The volume is estimated to be 100x the amount of extracted from other aquifers since 1900. The above diagram indicates typical flow directions in a view of a simple confined or unconfined aquifer system. The system shows two aquifers with one aquitard between them, surrounded by the bedrock aquiclude, which is in contact with a gaining stream, the water table and unsaturated zone are also illustrated. An aquitard is a zone within the earth that restricts the flow of groundwater from one aquifer to another, an aquitard can sometimes, if completely impermeable, be called an aquiclude or aquifuge. Aquitards are composed of layers of clay or non-porous rock with low hydraulic conductivity. Groundwater can be found at every point in the Earths shallow subsurface to some degree. Saturated means the head of the water is greater than atmospheric pressure. The definition of the table is the surface where the pressure head is equal to atmospheric pressure. Unsaturated conditions occur above the table where the pressure head is negative
Aquifer
–
Center-pivot irrigated fields in
Kansas covering hundreds of square miles watered by the
Ogallala Aquifer
Aquifer
–
Typical aquifer cross-section
Aquifer
–
Diagram of a
water balance of the aquifer
Aquifer
–
Air
19.
Petroleum reservoir
–
A petroleum reservoir or oil and gas reservoir is a subsurface pool of hydrocarbons contained in porous or fractured rock formations. Petroleum reservoirs are broadly classified as conventional and unconventional reservoirs, in case of conventional reservoirs, the naturally occurring hydrocarbons, such as crude oil or natural gas, are trapped by overlying rock formations with lower permeability. While in unconventional reservoirs the rocks have high porosity and low permeability which keeps the hydrocarbons trapped in place, reservoirs are found using hydrocarbon exploration methods. Crude oil found in all oil reservoirs formed in the Earths crust from the remains of once-living things, crude oil is properly known as petroleum, and is used as fossil fuel. Evidence indicates that millions of years of heat and pressure changed the remains of plant and animal into oil. When theyre buried with the sediment and reach an adequate temperature. This transformation, this change, changes them into the liquid hydrocarbons that move and migrate, will become our oil and gas reservoir. Timing is also an important consideration, it is suggested that the Ohio River Valley could have had as much oil as the Middle East at one time, but that it escaped due to a lack of traps. The North Sea, on the hand, endured millions of years of sea level changes that successfully resulted in the formation of more than 150 oilfields. Although the process is generally the same, various environmental factors lead to the creation of a variety of reservoirs. Reservoirs exist anywhere from the surface to 30,000 ft below the surface and are a variety of shapes, sizes and ages. A trap forms when the forces driving the upward migration of hydrocarbons through a permeable rock cannot overcome the capillary forces of a sealing medium. The timing of trap formation relative to that of petroleum generation and migration is crucial to ensuring a reservoir can form, the trapping mechanisms for many petroleum reservoirs have characteristics from several categories and can be known as a combination trap. Structural traps are formed as a result of changes in the structure of the due to processes such as folding and faulting, leading to the formation of domes, anticlines. Examples of this kind of trap are a trap, a fault trap. They are more delineated and more prospective than their stratigraphic counterparts. Stratigraphic traps are formed as a result of lateral and vertical variations in the thickness, texture, examples of this type of trap are an unconformity trap, a lens trap and a reef trap. Hydrodynamic traps are a far less common type of trap and they are caused by the differences in water pressure, that are associated with water flow, creating a tilt of the hydrocarbon-water contact
Petroleum reservoir
20.
Limestone
–
Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral, forams and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate, about 10% of sedimentary rocks are limestones. The solubility of limestone in water and weak acid solutions leads to karst landscapes, most cave systems are through limestone bedrock. The first geologist to distinguish limestone from dolomite was Belsazar Hacquet in 1778, like most other sedimentary rocks, most limestone is composed of grains. Most grains in limestone are skeletal fragments of organisms such as coral or foraminifera. Other carbonate grains comprising limestones are ooids, peloids, intraclasts and these organisms secrete shells made of aragonite or calcite, and leave these shells behind when they die. Limestone often contains variable amounts of silica in the form of chert or siliceous skeletal fragment, some limestones do not consist of grains at all, and are formed completely by the chemical precipitation of calcite or aragonite, i. e. travertine. Secondary calcite may be deposited by supersaturated meteoric waters and this produces speleothems, such as stalagmites and stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular appearance, the primary source of the calcite in limestone is most commonly marine organisms. Some of these organisms can construct mounds of rock known as reefs, below about 3,000 meters, water pressure and temperature conditions cause the dissolution of calcite to increase nonlinearly, so limestone typically does not form in deeper waters. Limestones may also form in lacustrine and evaporite depositional environments, calcite can be dissolved or precipitated by groundwater, depending on several factors, including the water temperature, pH, and dissolved ion concentrations. Calcite exhibits a characteristic called retrograde solubility, in which it becomes less soluble in water as the temperature increases. Impurities will cause limestones to exhibit different colors, especially with weathered surfaces, Limestone may be crystalline, clastic, granular, or massive, depending on the method of formation. Crystals of calcite, quartz, dolomite or barite may line small cavities in the rock, when conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together, or it can fill fractures. Travertine is a banded, compact variety of limestone formed along streams, particularly there are waterfalls. Calcium carbonate is deposited where evaporation of the leaves a solution supersaturated with the chemical constituents of calcite. Tufa, a porous or cellular variety of travertine, is found near waterfalls, coquina is a poorly consolidated limestone composed of pieces of coral or shells. During regional metamorphism that occurs during the building process, limestone recrystallizes into marble
Limestone
–
Limestone outcrop in the
Torcal de Antequera nature reserve of
Málaga, Spain
Limestone
–
Limestone quarry at
Cedar Creek, Virginia, USA
Limestone
–
Cutting the limestone blocks at a quarry in
Gozo,
Malta
Limestone
–
Limestone as building material
21.
Earthquake
–
An earthquake is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earths lithosphere that creates seismic waves. Earthquakes can range in size from those that are so weak that they cannot be felt to those violent enough to people around. The seismicity or seismic activity of an area refers to the frequency, type, Earthquakes are measured using measurements from seismometers. The moment magnitude is the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe and these two scales are numerically similar over their range of validity. Magnitude 3 or lower earthquakes are mostly imperceptible or weak and magnitude 7 and over potentially cause damage over larger areas. The largest earthquakes in historic times have been of magnitude slightly over 9, intensity of shaking is measured on the modified Mercalli scale. The shallower an earthquake, the damage to structures it causes. At the Earths surface, earthquakes manifest themselves by shaking and sometimes displacement of the ground, when the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides, and occasionally volcanic activity, in its most general sense, the word earthquake is used to describe any seismic event — whether natural or caused by humans — that generates seismic waves. Earthquakes are caused mostly by rupture of faults, but also by other events such as volcanic activity, landslides, mine blasts. An earthquakes point of rupture is called its focus or hypocenter. The epicenter is the point at ground level directly above the hypocenter, tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. The sides of a fault move past each other smoothly and aseismically only if there are no irregularities or asperities along the surface that increase the frictional resistance. Most fault surfaces do have such asperities and this leads to a form of stick-slip behavior, once the fault has locked, continued relative motion between the plates leads to increasing stress and therefore, stored strain energy in the volume around the fault surface. This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the portion of the fault. This energy is released as a combination of radiated elastic strain seismic waves, frictional heating of the fault surface and this process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the elastic-rebound theory. It is estimated that only 10 percent or less of a total energy is radiated as seismic energy. Most of the energy is used to power the earthquake fracture growth or is converted into heat generated by friction
Earthquake
–
Global plate tectonic movement
Earthquake
–
Global earthquake
epicenters, 1963–1998
Earthquake
–
Aerial photo of the San Andreas Fault in the
Carrizo Plain, northwest of Los Angeles
Earthquake
–
Collapsed Gran Hotel building in the
San Salvador metropolis, after the shallow
1986 San Salvador earthquake during mid civil war El Salvador.
22.
Quartzite
–
Quartzite is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone. Sandstone is converted into quartzite through heating and pressure related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in shades of pink. Other colors, such as yellow, green, blue and orange, are due to other minerals, when sandstone is cemented to quartzite, the individual quartz grains recrystallize along with the former cementing material to form an interlocking mosaic of quartz crystals. Most or all of the texture and sedimentary structures of the sandstone are erased by the metamorphism. The grainy, sandpaper-like surface becomes glassy in appearance, minor amounts of former cementing materials, iron oxide, silica, carbonate and clay, often migrate during recrystallization and metamorphosis. This causes streaks and lenses to form within the quartzite, orthoquartzite is a very pure quartz sandstone composed of usually well-rounded quartz grains cemented by silica. Orthoquartzite is often 99% SiO2 with only minor amounts of iron oxide and trace resistant minerals such as zircon, rutile. Although few fossils are present, the original texture and sedimentary structures are preserved. The term is traditionally used for quartz-cemented quartz arenites. Quartzite is very resistant to weathering and often forms ridges. The nearly pure silica content of the rock provides little for soil, therefore, because of its hardness and angular shape, crushed quartzite is often used as railway ballast. Quartzite is a stone and may be used to cover walls, as roofing tiles, as flooring. Its use for countertops in kitchens is expanding rapidly and it is harder and more resistant to stains than granite. Crushed quartzite is used in road construction. High purity quartzite is used to produce ferrosilicon, industrial silica sand, during the Paleolithic quartzite was used, in addition to flint, quartz, and other lithic raw materials, for making stone tools. Quartzite is also found in the Morenci Copper Mine in Arizona, the town of Quartzsite in western Arizona derives its name from the quartzites in the nearby mountains in both Arizona and Southeastern California. A glassy vitreous quartzite has been described from the Belt Supergroup in the Coeur d’Alene district of northern Idaho, in the United Kingdom, a craggy ridge of quartzite called the Stiperstones runs parallel with the Pontesford-Linley fault,6 km north-west of the Long Mynd in south Shropshire
Quartzite
–
Blue Quartzite from
Maurienne valley in the
French Alps
Quartzite
–
Quartzite has a grainy, sandpaper-like surface which becomes glassy in appearance
Quartzite
–
Abandoned quartzite mine in
Kakwa Provincial Park, British Columbia, Canada
Quartzite
–
Quartzite biface
hand axe from
Stellenbosch, South Africa
23.
Metamorphism
–
Metamorphism is the change of minerals or geologic texture in pre-existing rocks, without the protolith melting into liquid magma. The change occurs primarily due to heat, pressure, and the introduction of chemically active fluids, the chemical components and crystal structures of the minerals making up the rock may change even though the rock remains a solid. Changes at or just beneath Earths surface due to weathering and/or diagenesis are not classified as metamorphism, Metamorphism typically occurs between diagenesis, and melting. Three types of metamorphism exist, contact, dynamic, and regional, Metamorphism produced with increasing pressure and temperature conditions is known as prograde metamorphism. Conversely, decreasing temperatures and pressure characterize retrograde metamorphism, Metamorphic rocks can change without melting. When pressure is applied, somewhat flattened grains that orient in the same direction have a stable configuration. The upper boundary of metamorphic conditions is related to the onset of melting processes in the rock, the maximum temperature for metamorphism is typically 700 –900 °C, depending on the pressure and on the composition of the rock. Migmatites are rocks formed at this limit, which contain pods. Since the 1980s it has recognized that rocks are rarely dry enough. Conditions producing widespread regionally metamorphosed rocks occur during an orogenic event, the collision of two continental plates or island arcs with continental plates produce the extreme compressional forces required for the metamorphic changes typical of regional metamorphism. These orogenic mountains are eroded, exposing the intensely deformed rocks typical of their cores. The conditions within the slab as it plunges toward the mantle in a subduction zone also produce regional metamorphic effects. The techniques of structural geology are used to unravel the collisional history, regional metamorphism can be described and classified into metamorphic facies or metamorphic zones of temperature/pressure conditions throughout the orogenic terrane. Contact metamorphism occurs typically around intrusive igneous rocks as a result of the increase caused by the intrusion of magma into cooler country rock. The area surrounding the intrusion where the contact metamorphism effects are present is called the metamorphic aureole, contact metamorphic rocks are usually known as hornfels. Rocks formed by contact metamorphism may not present signs of deformation and are often fine-grained. Contact metamorphism is greater adjacent to the intrusion and dissipates with distance from the contact, the size of the aureole depends on the heat of the intrusion, its size, and the temperature difference with the wall rocks. Dikes generally have small aureoles with minimal metamorphism whereas large ultramafic intrusions can have significantly thick, the metamorphic grade of an aureole is measured by the peak metamorphic mineral which forms in the aureole
Metamorphism
–
A metamorphic aureole in the Henry Mountains, Utah. The greyish rock on top is the igneous intrusion, consisting of porphyritic granodiorite from the
Henry Mountains laccolith, and the pinkish rock on the bottom is the sedimentary country rock, a siltstone. In between, the metamorphosed siltstone is visible as both the dark layer (~5cm thick) and the pale layer below it.
Metamorphism
–
Schematic representation of a metamorphic reaction. Abbreviations of minerals: act =
actinolite; chl =
chlorite; ep =
epidote; gt =
garnet; hbl =
hornblende; plag =
plagioclase. Two minerals represented in the figure do not participate in the reaction, they can be
quartz and
K-feldspar. This reaction takes place in nature when a rock goes from
amphibolite facies to
greenschist facies.
Metamorphism
–
Metamorphic Facies with regard to temperature and pressure
24.
Orogenic belts
–
An Orogeny is an event that leads to a large structural deformation of the Earths lithosphere due to the interaction between tectonic plates. Orogens or orogenic belts develop when a plate is crumpled and is pushed upwards to form mountain ranges. Orogeny is the mechanism by which mountains are built on continents. The word orogeny comes from Ancient Greek, though it was used before him, the term was employed by the American geologist G. K. Gilbert in 1890 to describe the process of mountain building as distinguished from epeirogeny. Formation of an orogen is accomplished in part by the processes of subduction or convergence of two or more continents. Orogeny usually produces long arcuate structures, known as orogenic belts, generally, orogenic belts consist of long parallel strips of rock exhibiting similar characteristics along the length of the belt. Orogenic belts are associated with zones, which consume crust, produce volcanoes. Geologists attribute the arcuate structure to the rigidity of the descending plate and these island arcs may be added to a continent during an orogenic event. The processes of orogeny can take tens of millions of years, frequently, rock formations that undergo orogeny are severely deformed and undergo metamorphism. Orogenic processes may push deeply buried rocks to the surface, sea-bottom and near-shore material may cover some or all of the orogenic area. If the orogeny is due to two continents colliding, very high mountains can result, an orogenic event may be studied, as a tectonic structural event, as a geographical event, and as a chronological event. The foreland basin forms ahead of the orogen due mainly to loading and resulting flexure of the lithosphere by the mountain belt. The basin migrates with the front and early deposited foreland basin sediments become progressively involved in folding and thrusting. Sediments deposited in the basin are mainly derived from the erosion of the actively uplifting rocks of the mountain range. The fill of many such shows an change in time from deepwater marine through shallow water to continental sediments. Although orogeny involves plate tectonics, the tectonic forces result in a variety of associated phenomena, including magmatism, metamorphism, crustal melting, what exactly happens in a specific orogen depends upon the strength and rheology of the continental lithosphere, and how these properties change during orogenesis. In addition to orogeny, the orogen is subject to other processes, for example, the Caledonian Orogeny refers to the Silurian and Devonian events that resulted from the collision of Laurentia with Eastern Avalonia and other former fragments of Gondwana. The Caledonian Orogen resulted from events and various others that are part of its peculiar orogenic cycle
Orogenic belts
–
Shield
Orogenic belts
–
Two processes that can contribute to an orogen. Top:
delamination by intrusion of hot
asthenosphere; Bottom:
Subduction of ocean crust. The two processes lead to differently located granites (bubbles in diagram), providing evidence as to which process actually occurred.
Orogenic belts
–
An example of
thin-skinned deformation (
thrust faulting) of the
Sevier Orogeny in
Montana. Note the white
Madison Limestone repeated, with one example in the foreground (that pinches out with distance) and another to the upper right corner and top of the picture.
Orogenic belts
–
Sierra Nevada Mountains (a result of delamination) as seen from the
International Space Station.
25.
Coral Pink Sand Dunes State Park
–
Coral Pink Sand Dunes State Park is a state park of Utah, USA, located between Mount Carmel Junction and Kanab, south and west of U. S. Highway 89 in southwestern Utah. The park features coral-hued sand dunes located beside red sandstone cliffs, the Dunes are formed from the erosion of pink-colored Navajo Sandstone surrounding the park. High winds passing through the notch between the Moquith and Moccasin Mountains pick up sand particles and then drop them onto the dunes because of the Venturi effect. The dunes are estimated to be between 10,000 and 15,000 years old, the park allows camping, hiking, off-road vehicle driving, and photography. There is an area of 265 acres, and the total grounds include 3,370 acres. It was established as a Utah state park in 1963, the Coral Pink Sand Dunes tiger beetle is an insect species that is endemic to the dunes, being found nowhere else in the world. This state park contains most of the individuals of a rare plant, Welshs milkweed. Coral Pink Sand Dunes State Park travel guide from Wikivoyage Official Coral Pink Sand Dunes State Park website
Coral Pink Sand Dunes State Park
–
The sand that makes up the pink colored dunes is derived from the
Navajo Sandstone
Coral Pink Sand Dunes State Park
–
Sand from the dunes: grains of
quartz with a
hematite coating providing the orange color.
Coral Pink Sand Dunes State Park
–
Coral Pink Sand Dunes tiger beetle (Cicindela albissima)
26.
Utah
–
The Utah Railway is a class III railroad operating in Utah and Colorado, and owned by Genesee & Wyoming Inc. The Utah Railway Company was incorporated on January 24,1912, with the name of Utah Coal Railway, shortened to Utah Railway in May of the same year. It was founded to haul coal from the mines to Provo, Utah, in reaction to company disappointment in the service and route of the existing Denver. In addition, the Utah Railway was the first to equip its air brakes with fourteen-pound tension springs instead of the standard seven-pound springs and these gondolas were known to the railroads employees as Battleships. Parent company Mueller Industries, a manufacturer of products, sold the Utah Railway in 2002 to Genesee & Wyoming Inc. a railroad holding company. As of January,2017, the no longer hauls coal. The Utah Railway also owns a railroad, the Salt Lake City Southern Railroad. In addition, switching services are provided in Ogden and elsewhere, the earliest logo was simply the words Utah Railway Company, spelled out on the locomotives and cabooses, and Utah Coal Route on the drop-bottom gondolas. On paper, however, the logo for many years was a circle with a white background. The wording and image in these circular logos changed over the years, the 1948 logo included the words Utah Railway surrounding a gondola with the initials U. C. R. The 1999 logo was an oval with an image of an SD diesel locomotive, in later years the symbol of the Utah Railway Company was the beehive, which is also the Utah state symbol. Genesee & Wyoming corporate website Trainwebs Utah Railway UtahRails. net Utah Railway page
Utah
–
Former Union Pacific CA-1
Caboose on display in
Helper. The Utah Railway purchased eight of these cabooses from the UP between 1918 and 1927.
Utah
27.
Hematite
–
Hematite, also spelled as haematite, is the mineral form of iron oxide, one of several iron oxides. Hematite crystallizes in the lattice system, and it has the same crystal structure as ilmenite. Hematite and ilmenite form a solid solution at temperatures above 950 °C. Hematite is colored black to steel or silver-gray, brown to reddish brown and it is mined as the main ore of iron. Varieties include kidney ore, martite, iron rose and specularite, while the forms of hematite vary, they all have a rust-red streak. Hematite is harder than iron, but much more brittle. Maghemite is a hematite- and magnetite-related oxide mineral, huge deposits of hematite are found in banded iron formations. Gray hematite is typically found in places that can have still standing water or mineral hot springs, the mineral can precipitate out of water and collect in layers at the bottom of a lake, spring, or other standing water. Hematite can also occur without water, however, usually as the result of volcanic activity, the name hematite is derived from the Greek word for blood αἷμα haima, due to the red coloration found in some varities of hematite. The color of hematite lends itself to use as a pigment, ochre is a clay that is colored by varying amounts of hematite, varying between 20% and 70%. Red ochre contains unhydrated hematite, whereas yellow ochre contains hydrated hematite, the principal use of ochre is for tinting with a permanent color. The red chalk writing of this mineral was one of the earliest in the history of humans, the powdery mineral was first used 164,000 years ago by the Pinnacle-Point man possibly for social purposes. Hematite residues are found in graves from 80,000 years ago. Near Rydno in Poland and Lovas in Hungary red chalk mines have been found that are from 5000 BC, rich deposits of hematite have been found on the island of Elba that have been mined since the time of the Etruscans. Adding to the surprise was a transition with a decrease in temperature at around 260 K to a phase with no net magnetic moment. The disappearance of the moment with a decrease in temperature at 260 K is caused by a change in the anisotropy which causes the moments to align along the c axis, in this configuration, spin canting does not reduce the energy. The magnetic properties of bulk hematite differ from their nanoscale counterparts, for example, the Morin transition temperature of hematite decreases with a decrease in the particle size. Two other end-members are referred to as protohematite and hydrohematite, enhanced magnetic coercivities for hematite have been achieved by dry-heating a 2-line ferrihydrite precursor prepared from solution
Hematite
–
Brazilian
trigonal hematite crystal
Hematite
–
Crystal structure of hematite
Hematite
–
Image mosaic from the Mars Exploration Rover Microscopic Imager shows Hematite
spherules partly embedded in rock at the Opportunity landing site. Image is ca. 5 cm (2 in) across.
Hematite
–
Hematite carving, 5 cm (2 in) long.
28.
Clastic rock
–
Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus, chunks and smaller grains of rock broken off other rocks by physical weathering. Geologists use the term clastic with reference to sedimentary rocks as well as to particles in sediment transport whether in suspension or as bed load, clastic sedimentary rocks are rocks composed predominantly of broken pieces or clasts of older weathered and eroded rocks. Clastic sediments or sedimentary rocks are classified based on size, clast and cementing material composition. The classification factors are often useful in determining a samples environment of deposition, an example clastic environment would be a river system in which the full range of grains being transported by the moving water consist of pieces eroded from solid rock upstream. Grain size varies from clay in shales and claystones, through silt in siltstones, sand in sandstones, the Krumbein phi scale numerically orders these terms in a logarithmic size scale. Siliciclastic rocks are clastic rocks that are composed almost exclusively of silicon. The composition of sedimentary rocks includes the chemical and mineralogical components of the framework as well as the cementing material that make up these rocks. Boggs divides them into four categories, major minerals, accessory minerals, rock fragments, major minerals can be categorized into subdivisions based on their resistance to chemical decomposition. Those that possess a great resistance to decomposition are categorized as stable, while those that do not are considered less stable, the most common stable mineral in siliciclastic sedimentary rocks is quartz. Quartz makes up approximately 65 percent of framework grains present in sandstones, less stable minerals present in this type of rocks are feldspars, including both potassium and plagioclase feldspars. Feldspars comprise a considerably lesser portion of framework grains and minerals and they only make up about 15 percent of framework grains in sandstones and 5% of minerals in shales. Clay mineral groups are present in mudrocks but can be found in other siliciclastic sedimentary rocks at considerably lower levels. Accessory minerals are associated with those whose presence in the rock are not directly important to the classification of the specimen and these generally occur in smaller amounts in comparison to the quartz, and feldspars. Furthermore, those that do occur are generally heavy minerals or coarse grained micas, rock fragments also occur in the composition of siliciclastic sedimentary rocks and are responsible for about 10 -15 percent of the composition of sandstone. They generally make up most of the gravel size particles in conglomerates, though they sometimes are, rock fragments are not always sedimentary in origin. They can also be metamorphic or igneous, chemical cements vary in abundance but are predominantly found in sandstones. The two major types, are based and carbonate based
Clastic rock
–
A
thin section of a clast (sand grain), derived from a
basalt scoria.
Vesicles (air bubbles) can be seen throughout the clast. Plane light above, cross-
polarized light below. Scale box is 0.25 mm
Clastic rock
–
Claystone from
Montana
Clastic rock
–
Conglomerate
Clastic rock
–
Breccia. Notice the angular nature of the large clasts
29.
Chalk
–
Chalk is a soft, white, porous, sedimentary carbonate rock, a form of limestone composed of the mineral calcite. Calcite is a salt called calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the accumulation of minute calcite shells shed from micro-organisms called coccolithophores. Flint is very common as bands parallel to the bedding or as embedded in chalk. It is probably derived from sponge spicules or other organisms as water is expelled upwards during compaction. Flint is often deposited around larger fossils such as Echinoidea which may be silicified, Chalk as seen in Cretaceous deposits of Western Europe is unusual among sedimentary limestones in the thickness of the beds. Most cliffs of chalk have very few obvious bedding planes unlike most thick sequences of such as the Carboniferous Limestone or the Jurassic oolitic limestones. This presumably indicates very stable conditions over tens of millions of years, Chalk has greater resistance to weathering and slumping than the clays with which it is usually associated, thus forming tall steep cliffs where chalk ridges meet the sea. Chalk hills, known as chalk downland, usually form where bands of chalk reach the surface at an angle, because chalk is well jointed it can hold a large volume of ground water, providing a natural reservoir that releases water slowly through dry seasons. Chalk is mined from chalk deposits both above ground and underground, Chalk mining boomed during the Industrial Revolution, due to the need for chalk products such as quicklime and bricks. Abandoned chalk mines remain a popular tourist attraction due to their massive expanse, the Chalk Group is a European stratigraphic unit deposited during the late Cretaceous Period. It forms the famous White Cliffs of Dover in Kent, England, the Champagne region of France is mostly underlain by chalk deposits, which contain artificial caves used for wine storage. Some of the highest chalk cliffs in the occur at Jasmund National Park in Germany. Ninety million years ago what is now the chalk downland of Northern Europe was ooze accumulating at the bottom of a great sea. Chalk was one of the earliest rocks made up of particles to be studied under the electron microscope. Their shells were made of calcite extracted from the rich sea-water, as they died, a substantial layer gradually built up over millions of years and, through the weight of overlying sediments, eventually became consolidated into rock. Later earth movements related to the formation of the Alps raised these former sea-floor deposits above sea level, the chemical composition of chalk is calcium carbonate, with minor amounts of silt and clay. It is formed in the sea by plankton, which fall to the sea floor and are then consolidated and compressed during diagenesis into chalk rock
Chalk
–
The Needles, situated off the
Isle of Wight, are part of the extensive
Southern England Chalk Formation.
Chalk
–
"Nitzana Chalk curves" situated at Western
Negev,
Israel are chalk deposits formed at the
Mesozoic era's
Tethys Ocean
Chalk
–
Former underground chalk
quarry in
Meudon, France
Chalk
–
Open chalk pit, Seale, Surrey, UK
Saunders_Quarry-1.jpg)
