Geology

Geology

WAQAR HUSSAIN

CHINA UNIVERSITY OF PETROLEUM

 Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary roc Gneissic rocks are usually medium- to coarse-foliated and largely recrystallized but do not carry large quantities of micas, chlorite or other platy minerals .

Gneiss

Marble is a non foliated metamorphic rock resulting from the metamorphism of limestone, composed mostly of calcite (a crystalline form of calcium carbonate, CaCO3). It is extensively used for sculpture, as a building material, and in many other applications.

Marble

Migmatite is a rock at the frontier between igneous and metamorphic rocks. They can also be known as diatexite.

Migmatites form under extreme temperature conditions during prograde metamorphism, where partial melting occurs in pre-existing rocks. Migmatites are not crystallized from a totally molten material, and are not generally the result of solid-state reactions. Migmatites are composed of a leucosome, new material crystallized from incipient melting, and a mesosome, old material that resisted melting.

Migmatite

Gabbro refers to a large group of dark, coarse-grained, intrusive mafic igneous rocks chemically equivalent to basalt. The rocks are plutonic, formed when molten magma is trapped beneath the Earth's surface and cools into a crystalline mass.

The vast majority of the Earth's surface is underlain by gabbro within the oceanic crust, produced by basalt magmatism at mid-ocean ridges.

Gabbro

Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granites usually have a medium to coarse grained texture. Occasionally some individual crystals (phenocrysts) are larger than the groundmass in which case the texture is known as porphyritic. A granitic rock with a porphyritic texture is sometimes known as a porphyry.

Granite

Dolostone or dolomite rock is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite. In old U.S.G.S. publications it was referred to as magnesian limestone. Most dolostone formed as a magnesium replacement of limestone or lime mud prior to lithification

Dolostone

Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. The result is a foliated rock in which the foliation may not correspond to the original sedimentary layering. Slate is frequently grey in color, especially when seen en masse covering roofs.

Slate

Labradorite ((Ca,Na)(Al,Si)4O8), a feldspar mineral, is an intermediate to calcic member of the plagioclase series. It is usually defined as having "%An" (anorthite) between 50 and 70. The specific gravity ranges from 2.71 to 2.74. The streak is white, like most silicates

Labradorite

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