Rocks

Rocks are mineral assemblages. They compose of minerals or rock fragments which come together. According to the formation conditions and origins, the rocks are divided into three main groups as magmatic, metamorphic and sedimentary.

Magmatic Rocks

Magmatic rocks originate by cooling and by the solidification of magma or lava. Magma can emplace at depth, near surface or at the surface within the crust.

Plutonic Rocks

If the cooling and solidification of magma occur at depths, the resulting rocks are called plutonic rocks (eg. granite).

Volcanic Rocks

If the cooling and solidification of magma occur at the surface, the resulting rocks are called volcanic rocks (eg. basalt).

Vein Rocks

If the cooling and solidification of magma occur near surface, the resulting rocks are called vein rocks (eg. diabase).

Sedimentary Rocks

Sedimentary rocks can be formed by the disintegration, transportation, accumulation and calcification of previously formed rocks, as well as organisms that have lived in the past. This rock group usually shows a bedded structure. Three groups are separated as clastic, chemical and organic (biochemical) sedimentary rocks.

Conglomerate
(Clastic Sedimantary Rock)

 

Limestone
(Chemical Sedimentary Rock)

 

Coal
(Organic Sedimentary Rock)

 

Metamorphic Rocks

These rocks are formed by recrystallization of minerals under high pressures and temperatures.

Slate: It is a group of very small grain sized (<1mm) metamorphic rocks formed under the effect of very low grade metamorphism. 

Phyllite: This rock forms under the effect of low grade metamorphism. It is a fine grain sized (1-2 mm) rock with a weak foliation.

Schist: It is a rock which contains medium-coarse-grained (2-10 mm) minerals that exhibit foliation in the rock due to pressure and temperature effects.

Gneiss: It is a coarse-grained (10-15 mm) metamorphic rock which shows a distinctive banded foliation due to its high-grade metamorphism and is generally composed of minerals such as quartz, feldspar, mica and amphibole.

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