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Petrology Reference Libraries

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Biotite
2005-05-26 12:03:39

Biotite is a common phyllosilicate mineral that contains potassium, magnesium, iron and aluminium. It is sometimes called "iron mica" and is found in granitic rocks, gneisses, and schists. Like other mica minerals, biotite has a highly perfect basal cleavage, its flexible sheets easily flaking off. It has a hardness of 2.5 - 3, a specific gravity of 2.7 - 3.1, is colored greenish to brown or...

Chert
2005-05-26 11:30:45

Chert is a fine-grained silica-rich cryptocrystalline sedimentary rock that may contain small fossils. It varies greatly in color from white to black, but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements present in the rock, and both red and green are most often related to traces of iron (in its oxidized and reduced...

Chromite Iron Chromium Oxide
2005-05-26 11:26:59

Chromite, iron magnesium chromium oxide: (Fe,Mg)Cr2O4, is an oxide mineral belonging to the spinel group. Magnesium is always present in variable amounts, also aluminium and iron substitute for chromium. Chromite is found in peridotite and other layered ultramafic intrusive rocks and also found in metamorphic rocks such as serpentinites. Ore deposites of chromite form as early magmatic...

Conglomerate geology
2005-05-26 11:13:08

In geology, a conglomerate is a rock consisting of other stones that have been cemented together. Conglomerates are sedimentary rocks consisting of subangular clasts and are thus differentiated from breccias, which consist of angular clasts. Both conglomerates and breccias are characterized by clasts larger than sand (>2 mm). There are two varieties of conglomerate, defined by texture:...

Diorite
2005-05-26 11:01:52

Diorite is a grey to dark grey intermediate intrusive igneous rock composed principally of plagioclase feldspar (typically andesine), hornblende, and/or pyroxene. Varieties deficient in hornblende and other dark minerals are called leucodiorite. It is often described as "salt and pepper" when composed largely of light-colored minerals randomly interspersed with dark minerals. When olivine and...

Gabbro
2005-05-26 11:00:22

Gabbro is a dark, coarse-grained, intrusive igneous rock chemically equivalent to basalt. It is a plutonic rock, formed when molten magma is trapped beneath the Earth's surface and cools slowly into a hard, coarsely crystalline mass. It is dense, greenish or dark-colored and contains varied percentages of plagioclase feldspar, pyroxene, amphibole, and olivine (called olivine gabbro when olivine...

Garnierite
2005-05-26 10:59:02

Garnierite is a mineral composed of hydrous nickel silicates a member of the serpentine group with formula: (Ni,Mg)3Si2O5(OH). Népouite is a synonym. Garnierite is important as a source of nickel and is mined from laterite deposits which are formed by intense weathering and secondary enrichment of ultramafic igneous rocks.

Kyanite
2005-05-26 09:41:33

The mineral kyanite is an aluminium silicate of the sillimanite group (along with andalusite and sillimanite), also called alumino-silicate. It has the formula Al2O3·SiO2 (Al2SiO5). Its hardness varies widely depending on its crystallographic direction, from 5 to 7.5, and it has a specific gravity of 3.56-3.67. It is translucent, usually blue, but possibly white, gray, green, or black. It...

Marble
2005-05-26 08:52:39

Marble is metamorphosed limestone, composed of fairly pure calcite (a crystalline form of calcium carbonate, CaCO3). It is extensively used for sculpture, as a building material, and in many other applications. Faux marble or faux marbling is a wall painting technique that imitates the color patterns of real marble (not to be confused with paper marbling). Marble dust can be combined with...

Muscovite
2005-05-26 08:35:42

Muscovite, also known as potash mica, is a phyllosilicate mineral of aluminium and potassium. It has a highly perfect basal cleavage yielding remarkably thin laminae (sheets), which are often highly elastic. Muscovite has a hardness of 2 - 2.25 and a specific gravity of 2.76 - 3. It can be colorless or tinted through grays, browns, greens, yellows, or rarely violet or red, and can be...

Word of the Day
snash
  • To talk saucily.
  • Insolent, opprobrious language; impertinent abuse.
This word is Scots in origin and probably imitative.