1.
Gabbro
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Gabbro refers to a large group of dark, often phaneritic, mafic intrusive igneous rocks chemically equivalent to basalt. It forms when magma is trapped beneath the Earths surface. Much of the Earths oceanic crust is made of gabbro, formed at mid-ocean ridges, Gabbro is also found as plutons associated with continental volcanism. Due to its variant nature, the term gabbro may be applied loosely to a range of intrusive rocks. The term gabbro was used in the 1760s to name a set of types that were found in the ophiolites of the Apennine Mountains in Italy. Then, in 1809, the German geologist Christian Leopold von Buch used the term more restrictively in his description of these Italian ophiolitic rocks and he assigned the name gabbro to rocks that geologists nowadays would more strictly call metagabbro. Von Buch named gabbro after Gabbro, a village in Rosignano Marittimo municipality of Tuscany, Gabbro is dense, greenish or dark-colored and contains pyroxene, plagioclase, and minor amounts of amphibole and olivine. The pyroxene content is mostly clinopyroxene, generally augite, but small amounts of orthopyroxene may also be present, if the amount of orthopyroxene is more than 95% of the total pyroxene content, then the rock is termed norite. On the other hand, gabbro has more than 95% of its pyroxenes in the form of the monoclinic clinopyroxene/s, the calcium rich plagioclase feldspar and pyroxene content vary between 10% - 90% in gabbro. If more than 90% plagioclase is present, then the rock is an anorthosite, if on the other hand, the rock contains more than 90% pyroxenes, it is termed pyroxenite. Gabbro may also contain amounts of olivine, amphibole and biotite. The quartz content in gabbro is less than 5% of total volume, quartz gabbros or monzogabbros are also known to occur, for example the cizlakite at Pohorje in northeastern Slovenia, and are probably derived from magma that was over-saturated with silica. Gabbros contain minor amounts, typically a few percent, of iron-titanium oxides such as magnetite, ilmenite, Gabbro is generally coarse grained, with crystals in the size range of 1 mm or greater. Finer grained equivalents of gabbro are called diabase, although the term microgabbro is often used when extra descriptiveness is desired, Gabbro may be extremely coarse grained to pegmatitic, and some pyroxene-plagioclase cumulates are essentially coarse grained gabbro, some may exhibit acicular crystal habits. Gabbro is usually equigranular in texture, although it may be porphyritic at times, cumulate gabbros are more properly termed pyroxene-plagioclase adcumulate. Gabbro is an part of the oceanic crust, and can be found in many ophiolite complexes as parts of zones III. Long belts of gabbroic intrusions are typically formed at proto-rift zones and around ancient rift zone margins, mantle plume hypotheses may rely on identifying mafic and ultramafic intrusions and coeval basalt volcanism. It is better to base a rock definition on descriptive characteristics of the rather than how or where it was formed
2.
Sierra Nevada (U.S.)
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The Sierra Nevada is a mountain range in the Western United States, between the Central Valley of California and the Basin and Range Province. The vast majority of the lies in the state of California. The Sierra runs 400 miles north-to-south, and is approximately 70 miles across east-to-west, the Sierra is home to three national parks, twenty wilderness areas, and two national monuments. These areas include Yosemite, Sequoia, and Kings Canyon National Parks, the character of the range is shaped by its geology and ecology. More than one hundred years ago during the Nevadan orogeny. The range started to uplift four M. A. ago, the uplift caused a wide range of elevations and climates in the Sierra Nevada, which are reflected by the presence of five life zones. Uplift continues due to faulting caused by forces, creating spectacular fault block escarpments along the eastern edge of the southern Sierra. The Sierra Nevada has a significant history, the California Gold Rush occurred in the western foothills from 1848 through 1855. Due to inaccessibility, the range was not fully explored until 1912, the Sierra Nevada lies in Central and Eastern California, with a very small but historically important spur extending into Nevada. West-to-east, the Sierra Nevadas elevation increases gradually from 1,000 feet in the Central Valley to an height of about 10,500 feet at its crest only 50–75 miles to the east. The east slope forms the steep Sierra Escarpment, unlike its surroundings, the range receives a substantial amount of snowfall and precipitation due to orographic lift. The Sierra Nevada stretches from the Susan River and Fredonyer Pass in the north to Tehachapi Pass in the south and it is bounded on the west by Californias Central Valley and on the east by the Basin and Range Province. The geographical boundary between the Sierra and the Cascades is virtually indistinguishable, with the Fredonyer Pass designation being traditional, physiographically, the Sierra is a section of the Cascade-Sierra Mountains province, which in turn is part of the larger Pacific Mountain System physiographic division. The range is drained on its western slope by the Central Valley watershed, the northern third of the western Sierra is part of the Sacramento River watershed, and the middle third is drained by the San Joaquin River. The eastern slope watershed of the Sierra is much narrower, its rivers flow out into the endorheic Great Basin of eastern California and western Nevada. Although none of the eastern rivers reach the sea, many of the streams from Mono Lake southwards are diverted into the Los Angeles Aqueduct which provides water to Southern California, the height of the mountains in the Sierra Nevada increases gradually from north to south. Between Fredonyer Pass and Lake Tahoe, the range from 5,000 feet to more than 9,000 feet. The crest near Lake Tahoe is roughly 9,000 feet high, farther south, the highest peak in Yosemite National Park is Mount Lyell
3.
Olivine
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The mineral olivine is a magnesium iron silicate with the formula 2SiO4. Thus it is a type of nesosilicate or orthosilicate and it is a common mineral in the Earths subsurface but weathers quickly on the surface. The ratio of magnesium and iron varies between the two endmembers of the solid solution series, forsterite and fayalite, compositions of olivine are commonly expressed as molar percentages of forsterite and fayalite. Forsterite has a high melting temperature at atmospheric pressure, almost 1,900 °C. The melting temperature varies smoothly between the two endmembers, as do other properties, olivine incorporates only minor amounts of elements other than oxygen, silicon, magnesium and iron. Manganese and nickel commonly are the elements present in highest concentrations. Olivine gives its name to the group of minerals with a structure which includes tephroite, monticellite and kirschsteinite. It has a structure similar to magnetite but uses one quadravalent. Olivine gemstones are called peridot and chrysolite, olivine is named for its typically olive-green color, though it may alter to a reddish color from the oxidation of iron. Translucent olivine is sometimes used as a gemstone called peridot, some of the finest gem-quality olivine has been obtained from a body of mantle rocks on Zabargad island in the Red Sea. Olivine occurs in mafic and ultramafic igneous rocks and as a primary mineral in certain metamorphic rocks. Mg-rich olivine crystallizes from magma that is rich in magnesium and low in silica and that magma crystallizes to mafic rocks such as gabbro and basalt. Ultramafic rocks such as peridotite and dunite can be left after extraction of magmas. Olivine and high pressure structural variants constitute over 50% of the Earths upper mantle, the metamorphism of impure dolomite or other sedimentary rocks with high magnesium and low silica content also produces Mg-rich olivine, or forsterite. In contrast, Mg-rich olivine does not occur stably with silica minerals, Mg-rich olivine is stable to pressures equivalent to a depth of about 410 km within Earth. Mg-rich olivine has also discovered in meteorites, on the Moon and Mars, falling into infant stars. Such meteorites include chondrites, collections of debris from the early Solar System, the spectral signature of olivine has been seen in the dust disks around young stars. The tails of comets often have the signature of olivine
4.
Weathering
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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
5.
Iddingsite
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Iddingsite is a microcrystalline rock that is derived from alteration of olivine. It is usually studied as a mineral, and consists of a mixture of remnant olivine, clay minerals, debates over iddingsites non-definite crystal structure caused it to be de-listed as an official mineral by the IMA, thus it is properly referred to as a rock. Because iddingsite is constantly transforming it does not have a structure or a definite chemical composition. The chemical formula for iddingsite has been approximated as MgO * Fe2O3 *4 H2O where MgO can be substituted by CaO, the geologic occurrence of iddingsite is limited to extrusive or subvolcanic rocks that are formed by injection of magma near the surface. It is absent from deep-seated rocks and is found on meteorites, as it has been found on Martian meteorites, its ages have been calculated to obtain absolute ages when liquid water was at or near the surface of Mars. Iddingsite is a pseudomorph, and during the process the olivine crystals had their internal structure or chemical composition changed. This is not true for all phases of the alteration of olivine because the arrangement becomes distorted. Iddingsite has a composition that is transforming from the original olivine passing though many stages of structural and chemical change. Iddingsite has been a subject researched in recent years because of its presence in the Martian meteorites, the formation of iddingsite requires liquid water, giving scientists an estimate as to when there has been liquid water on Mars. Potassium-argon dating of the samples showed that Mars had water on its surface anywhere from 1300 Ma to 650 Ma ago. Iddingsite is a mineral that lacks a definite composition, so exact compositions cannot be calculated. An approximated composition for an end product of iddingsite has been calculated as being SiO2 = 16%, Al2O3 = 8%, Fe2O3 = 62%. Throughout the alteration process of olivine, there is a decrease in SiO2, FeO and MgO, the chemical process associated with the alteration consists of the addition of Fe2O3 and the removal of MgO. The chemical formula for iddingsite is approximated as MgO * Fe2O3 *4 H2O where MgO can be substituted by CaO by a ratio of 1,4, there are also some trace constituents of Na2O and K2O that enter iddingsite as the alteration process progresses. The geologic occurrence of Iddingsite is limited to extrusive or hypabyssal rocks, Iddingsite is an epimagmatic mineral derived during the final cooling of lava in which it occurs from a reaction between gases, water and olivine. The formation of iddingsite is not dependent on the composition of the olivine. It is however dependent on conditions, hydration and the magma from which iddingsite forms must be rich in water vapor. The alteration of olivine to iddingsite occurs in an oxidizing environment under low pressure
6.
Rock (geology)
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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
7.
Geology
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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
8.
Inclusion (mineral)
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In mineralogy, an inclusion is any material that is trapped inside a mineral during its formation. In gemology, an inclusion is a characteristic enclosed within a gemstone, according to Huttons law of inclusions, fragments included in a host rock are older than the host rock itself. Inclusions are usually other minerals or rocks, but may also be water, liquid or vapor inclusions are known as fluid inclusions. In the case of amber it is possible to find insects and plants as inclusions, the analysis of atmospheric gas bubbles as inclusions in ice cores is an important tool in the study of climate change. A xenolith is a rock which has been picked up by a lava flow. Melt inclusions form when bits of melt become trapped inside crystals as they form in the melt, inclusions are one of the most important factors when it comes to gem valuation. In many gemstones, such as diamonds, inclusions affect the clarity of the gem, in some gems, however, such as star sapphires, the inclusion actually increases the value of the gem. Many colored gemstones, such as amethyst, emerald, and sapphire, are expected to have inclusions, colored gemstones are categorized into three types as follows, Type I colored gems include gems with very little or no inclusions. They include aquamarines, topaz and zircon, Type II colored gems include those that often have a few inclusions. They include sapphire, ruby, garnet and spinel, Type III colored gems include those that almost always have inclusions. Gems in this category include emerald and tourmaline, the term inclusion is also used in the context of metallurgy and metals processing. During the melt stage of processing hard particles such as oxides can enter or form in the metal which are subsequently trapped when the melt solidifies. The term is used negatively such as when the particle could act as a fatigue crack nucleator or as an area of high stress intensity
9.
Igneous rock
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Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava, the magma can be derived from partial melts of existing rocks in either a planets mantle or crust. Typically, the melting is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, Igneous and metamorphic rocks make up 90–95% of the top 16 km of the Earths crust by volume. Igneous rocks form about 15% of the Earths current land surface, most of the Earths oceanic crust is made of igneous rock. In terms of modes of occurrence, igneous rocks can be either intrusive or extrusive, the mineral grains in such rocks can generally be identified with the naked eye. Intrusive rocks can also be classified according to the shape and size of the intrusive body, typical intrusive formations are batholiths, stocks, laccoliths, sills and dikes. When the magma solidifies within the earths crust, it cools slowly forming coarse textured rocks, such as granite, gabbro, the central cores of major mountain ranges consist of intrusive igneous rocks, usually granite. When exposed by erosion, these cores may occupy huge areas of the Earths surface, intrusive igneous rocks that form at depth within the crust are termed plutonic rocks and are usually coarse-grained. Intrusive igneous rocks that form near the surface are termed subvolcanic or hypabyssal rocks, hypabyssal rocks are less common than plutonic or volcanic rocks and often form dikes, sills, laccoliths, lopoliths, or phacoliths. Extrusive igneous rocks, also known as rocks, are formed at the crusts surface as a result of the partial melting of rocks within the mantle. Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks and they are formed by the cooling of molten magma on the earths surface. The magma, which is brought to the surface through fissures or volcanic eruptions, hence such rocks are smooth, crystalline and fine-grained. Basalt is an extrusive igneous rock and forms lava flows, lava sheets. Some kinds of basalt solidify to form long polygonal columns, the Giants Causeway in Antrim, Northern Ireland is an example. The molten rock, with or without suspended crystals and gas bubbles, is called magma and it rises because it is less dense than the rock from which it was created. When magma reaches the surface from beneath water or air, it is called lava, eruptions of volcanoes into air are termed subaerial, whereas those occurring underneath the ocean are termed submarine. Black smokers and mid-ocean ridge basalt are examples of volcanic activity
10.
Lava
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Lava is the molten rock expelled by a volcano during an eruption. The resulting rock after solidification and cooling is called lava. The molten rock is formed in the interior of planets, including Earth. The source of the heat melts the rock within the earth is geothermal energy. When first erupted from a vent, lava is a liquid usually at temperatures from 700 to 1,200 °C. A lava flow is an outpouring of lava, which is created during a non-explosive effusive eruption. When it has stopped moving, lava solidifies to form igneous rock, the term lava flow is commonly shortened to lava. Although lava can be up to 100,000 times more viscous than water, lava can flow great distances before cooling and solidifying because of its thixotropic, explosive eruptions produce a mixture of volcanic ash and other fragments called tephra, rather than lava flows. The word lava comes from Italian, and is derived from the Latin word labes which means a fall or slide. The first use in connection with extruded magma was apparently in an account written by Francesco Serao on the eruption of Vesuvius between May 14 and June 4,1737. Serao described a flow of lava as an analogy to the flow of water. The composition of almost all lava of the Earths crust is dominated by silicate minerals, mostly feldspars, olivine, pyroxenes, amphiboles, micas, igneous rocks, which form lava flows when erupted, can be classified into three chemical types, felsic, intermediate, and mafic. These classes are primarily chemical, however, the chemistry of lava also tends to correlate with the temperature, its viscosity. Felsic or silicic lavas such as rhyolite and dacite typically form lava spines, most silicic lava flows are extremely viscous, and typically fragment as they extrude, producing blocky autobreccias. Felsic magmas can erupt at temperatures as low as 650 to 750 °C, unusually hot rhyolite lavas, however, may flow for distances of many tens of kilometres, such as in the Snake River Plain of the northwestern United States. Intermediate or andesitic lavas are lower in aluminium and silica, and usually somewhat richer in magnesium, intermediate lavas form andesite domes and block lavas, and may occur on steep composite volcanoes, such as in the Andes. Poorer in aluminium and silica than felsic lavas, and also commonly hotter, greater temperatures tend to destroy polymerized bonds within the magma, promoting more fluid behaviour and also a greater tendency to form phenocrysts. Higher iron and magnesium tends to manifest as a darker groundmass, mafic or basaltic lavas are typified by their high ferromagnesian content, and generally erupt at temperatures in excess of 950 °C
11.
Quartz
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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
12.
Diamond
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Diamond is a metastable allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the rate from diamond to graphite is negligible at standard conditions. Diamond is renowned as a material with superlative physical qualities, most of which originate from the covalent bonding between its atoms. In particular, diamond has the highest hardness and thermal conductivity of any bulk material and those properties determine the major industrial application of diamond in cutting and polishing tools and the scientific applications in diamond knives and diamond anvil cells. Because of its extremely rigid lattice, it can be contaminated by very few types of impurities, such as boron, small amounts of defects or impurities color diamond blue, yellow, brown, green, purple, pink, orange or red. Diamond also has relatively high optical dispersion, most natural diamonds are formed at high temperature and pressure at depths of 140 to 190 kilometers in the Earths mantle. Carbon-containing minerals provide the source, and the growth occurs over periods from 1 billion to 3.3 billion years. Diamonds are brought close to the Earths surface through deep volcanic eruptions by magma, Diamonds can also be produced synthetically in a HPHT method which approximately simulates the conditions in the Earths mantle. An alternative, and completely different growth technique is chemical vapor deposition, several non-diamond materials, which include cubic zirconia and silicon carbide and are often called diamond simulants, resemble diamond in appearance and many properties. Special gemological techniques have developed to distinguish natural diamonds, synthetic diamonds. The word is from the ancient Greek ἀδάμας – adámas unbreakable, the name diamond is derived from the ancient Greek αδάμας, proper, unalterable, unbreakable, untamed, from ἀ-, un- + δαμάω, I overpower, I tame. Diamonds have been known in India for at least 3,000 years, Diamonds have been treasured as gemstones since their use as religious icons in ancient India. Their usage in engraving tools also dates to early human history, later in 1797, the English chemist Smithson Tennant repeated and expanded that experiment. By demonstrating that burning diamond and graphite releases the same amount of gas, the most familiar uses of diamonds today are as gemstones used for adornment, a use which dates back into antiquity, and as industrial abrasives for cutting hard materials. The dispersion of light into spectral colors is the primary gemological characteristic of gem diamonds. In the 20th century, experts in gemology developed methods of grading diamonds, four characteristics, known informally as the four Cs, are now commonly used as the basic descriptors of diamonds, these are carat, cut, color, and clarity. A large, flawless diamond is known as a paragon and these conditions are met in two places on Earth, in the lithospheric mantle below relatively stable continental plates, and at the site of a meteorite strike. The conditions for diamond formation to happen in the mantle occur at considerable depth corresponding to the requirements of temperature and pressure
