In a general classification, the three principal rock types may be differentiated as follows:

Loose rocks
Loose deposits from rivers and glaciers.

Sedimentary rocks
Compacted loose rocks whose rock components have different origins and dimensions and which are held together by a cement. They can be differentiated into clastic sedimentary rocks or biogenic sedimentary rocks, according to their origin.

Crystalline rocks
Rocks which are principally formed of crystallised material. Crystalline rocks can be classified according to origin as magmatic rocks or metamorphic rocks.