Which rock am I?

marble

I am formed by metamorphism of limestone or dolomite.

shale

I am the most abundant sedimentary rock.

granite

I compose most of Earth's continental crust.

gabbro

I am a coarse-grained rock that composes a large portion of the oceanic crust.

limestone

I am a sedimentary rock that is at least 50% calcium carbonate.

obsidian

I am an amorphous rock that has been used for making simple knives, axes, arrowheads, and other tools and weapons.