Rock classification

The classification of igneous rocks

Igneous rocks are classified according to the silica present in their chemical composition.

The classification of sedimentary rocks

Sedimentary rocks are usually divided into two main groups - clastic and non-clastic.

Clastic rocks are formed from fragments of pre-existing rocks that have been weathered, transported and deposited.

Non-clastic rocks are formed by chemical and biological action.

The classification of metamorphic rocks

Metamorphic rocks are classified according to the type of rock they originally were and the kind of metamorphism they have undergone. There are five types of metamorphism:

Metamorphism	Caused by
Thermal	Heat alone
Dynamic	Intense stress
Regional	Heat and pressure
Retrograde	Reversal of previous metamorphism
Autometamorphism	Cooling of igneous mass

The classification of meteorites

Four main types are usually recognised:
Type	Description
Siderites	Nickel-iron
Stony-irons	Metal and silicate
Stones	Silicate
Tektites	Glassy