THE THREE MAIN CATEGORIES OF ROCKS

THE THREE MAIN CATEGORIES OF ROCKS

- magma is the parent material, a molten material from deep within earth that cools and hardens. This is an exothermic process (heat is liberated) and involves a change of phase from the liquid to solid state.

-most abundant rocks

Hard and tough

There are many varieties of igneous rocks and they are given names based upon 2 things:A.TEXTURE-relates to the general appearance of an igneous rocks. The texture of an igneous rock is strongly affected by the rate of cooling of the magma that results in the formation of crystals. These crystals are actually minerals.

Usually, the slower the rate of cooling, the larger the crystals found in the rock resulting in a coarse-grained igneous rock. On the other hand, the faster the rate of cooling, the smaller the crystals are and resulting into a fine-grained igneous rock.

Coarse-grained varieties are considered phaneritic while fine-grained varieties are considered aphanitic.

b. Composition- Refers to the elements in the magma that directly affect the kind of mineral that is formed when the magma cools.

The composition of igneous is directly related to where the magma is formed. Magmas associated with crustal spreading are generally mafic while magmas associated with crustal compression and subduction are termed felsic.

Igneous rocks may differ in texture but they can be the same in terms of composition.

TYPES OF IGNEOUS ROCKS