Coal		classified principally according to the minerals they consist of and on their chemical composition
Quartzite		nonfoliated metamorphic rock resulting from the metamorphism of limestone
Gneis		currently known only on Earth where it forms a major part of continental crust.
Hornfel		It is usually gray to black and fine-grained due to rapid cooling of lava
Slate		fine-grained, foliated, homogeneous, metamorphic rock
Conglomerate		fine-grained metamorphic rock
Sandstone		rock composed of angular fragments of several minerals
Schist		a rock consisting of individual stones that have become cemented together
Diorite		Fine-grained aquifer
Halite		metamorphic rock with a high hardness
Basalt		the largest source of fuel for the generation of electricity world-wide
Rhyolite		The vast majority of the Earth's surface
Gabbro		textural term for a volcanic rock
Marble		can be considered as the extrusive equivalent to the plutonic granite rock
Breccia		esults from partial melting of a mafic rock above a subduction zone
Granite		name of a sedimentary carbonate rock
Pumice		a naturally occurring glass formed as an extrusive igneous rock
Obsidian		very resistant to chemical weathering and often forms ridges and resistant hilltops
Dolomite		commonly known as rock salt.