Types of Minerals and Rocks

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Look round. All that we see: the sand on the river beach and pebbles on the beach, and clay in the ravine there are rocks and minerals. The earth's crust consists of them.

There are about 3 thousand minerals and more than 1.5 thousand rocks in the earth's crust.

What is the Nature of the Body?

A mineral is a naturally occurring inorganic solid. It has a specific chemical composition and a characteristic crystal structure (J. Richard Wilson Minerals and Rocks, p. 8)

Minerals are a homogeneous body consisting of a single substance. For example, water, gold, quartz, feldspar, mica, rock salt, diamond and others. Minerals are solid, liquid and gaseous.

Pure naturally minerals occur relatively seldom. Most often, they are different compounds forming rocks.

Rocks is a combination of several minerals or other accumulations in large quantities in the earth's crust. For example, the granite rock consists of three minerals: quartz, mica, feldspar. The limestone forms a large concentration of calcite. Minerals and rocks have many properties that are different from each other: the color, gloss, hardness, presence of crystals.

Rocks are naturally occurring, coherent solids consisting of an aggregate of minerals. There are three main groups of rocks, classified on the basis of how they are formed:

- Igneous

- Sedimentary

- Metamorphic

Igneous rocks are formed when magma solidifies on the surface or in the depths of the earth's crust. They are as a result of magmatic one of the internal forces of the Earth. For internal magmatism formed rooted (deep) rocks. They are composed of crystals of various sizes depending on the depth (the closer to the surface of solidified magma, the small crystals). These rocks are granite and labradorite. (J. Richard Wilson Minerals and Rocks, p. 9)

The rocks are formed from lava or compressed volcanic ash. They do not have crystals. They are porous. For example, basalt, tuff, pumice.

Igneous rocks can be classified according to many criteria, such as texture, crystal or grain size, colour, mineralogy, chemical composition, mode of occurrence, and genesis Igneous rocks are classified by their content of essential minerals i.e. those that make up the bulk of the rock this is known as the mode of the rock. Minor amounts of accessory minerals are not considered

Two terms used in connection with grain size are:

- phaneritic:individual crystals can be distinguished with the naked eye.

- aphanitic:most of the individual crystals cannot be distinguished with the naked eye.

Igneous rocks are divided into two main groups on the basis of their field relations or on their grain size.

- plutonic crystallized at depth. Phaneritic. Average crystal or grain size > 5mm (coarse); 15mm (medium); 0.51mm (fine grained).

- volcanoic extruded at the surface of the Earth. Aphanitic. Grain size < 0.5mm (very fine grained).

Plutonic Rocks

Plutonic rocks are classified according to their modal mineral content i.e. actual mineral content in volume %. The classification (from 1976) is known as the Streckeisen system after the Austrian professor who was chairman of an international committee to systematise the naming of igneous rocks. Before this there was considerable international confusion and disagreement as to how igneous rocks should be named.

For the naming of plutonic rocks, five groups of minerals are used. These are:

- quartz

- alkali feldspar orthoclase, microcline, perthite, anorthoclase and albite (An0005)

- plagioclase (An05100)

- feldspathoid minerals or FOIDS nepheline, leucite, sodalite etc.

- mafic minerals. Mafic stands for Mg-Fe minerals and includes olivine, pyroxenes, amphiboles, micas, garnets, oxide and sulphide minerals etc.

Q, A, P and F are light coloured minerals. M are dark minerals. The percentage of dark minerals (%M) is often referred to as the COLOUR INDEX of a rock. (J. Richard Wilson Minerals and Rocks, p. 73-76)

Plutonic rocks are divided into groups depending on the content of dark minerals M.

M < 90%. In the rock dominated the light coloured (felsic) minerals. And they take up 100% rock composition.

M > 90%. In the rock dominated the dark. The rocks are ULTRAMAFIC.

Chemical analysis plays an important role in the classification of rocks of volcanic.

Sedimentary rocks are formed by the action of the temperature of air, water, living organisms and other processes occurring in the Earth's surface and in the depths of the seas and oceans.

An important mineral that does not break down is quartz. As they become buried, loose sediments (sand, silt, clay) become consolidated and form compact rocks sedimentary rocks. An example is consolidated clay that is called shale. Other sedimentary rocks form as a result of the precipitation of minerals from water; rock salt is an exampleOne of the most obvious features of sedimentary rocks is layering. (J. Richard Wilson Minerals and Rocks, p. 9)

There are four different types of sedimentary rocks:

- clastic (or detrital) consist of consolidated fragments

- biochemical consist of the shells of organisms

- organic consist of carbon-rich plant remains

- chemical consist of minerals deposited directly from hydrous solutions. (J. Richard Wilson Minerals and Rocks, p. 127)

- clastic rocks. They are resulting in the destruction of other rocks (sand, clay, pebbles, gravel, stones). They are called clastic because that every particle the rocks are fragments of other rocks.

- chemicals - are a consequence of deposition of solutes at the bottom of the oceans, seas and lakes. For example: potassium salt, limestone, etc.

- organic. For example: coal, chalk.

Metamorphic rocks are formed by metamorphism.

Metamorphism (in translation - "transformation"), - changes in the rocks at great depths under high pressure and temperature. For example, limestone is transformed into marble, sandstone - in quartz, granite - in gneiss, coal graphite.

There are two main groups of metamorphic rocks, those that are foliated and those that are not. Most non-foliated rocks have been subjected to the effects of temperature (under constant pressure), whereas foliated rocks have been deformed during heating. (J. Richard Wilson Minerals and Rocks, p. 145)

Most metamorphic rocks at the surface of the earth occur in the Precambrian shield areas (ancient continents) and mountain belts. The Precambrian shields are dominated by gneissic rocks. Mountain belts are formed as a result of continental collision. The young mountain belt that stretches roughly east-west from the Alps to the Himalayas was formed (and is still being formed) as a result of the collision of the African and Indian continental plates with the European and Asian continental plates. Gneissic areas represent the root zones of ancient mountain belts. (J. Richard Wilson Minerals and Rocks, p. 162)

Worked CitedWilson, J. Richard. Minerals and Rocks.BookBoon, 2010. Print.

 

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