Types of igneous rocks - Igneous Rocks Classified by Composition

Sedimentary rocks are formed from pre-existing rocks or pieces of once-living organisms.

Foliated means the parallel arrangement of certain mineral grains that gives the rock a striped appearance.

This type of igneous rock is often associated with its ultramafic cousin peridotite.

Breccia perhaps refers to a class of clastic sedimentary rocks.

This type of igneous rock forms when a body of rhyolite or obsidian, for one reason or another, has a relatively large amount of water.

What type of rocks are the hardest? An extrusive rock of the same composition as syenite is called trachyte.