(30).Methamorphic rocks classification.

What's the difference in these two rocks?

The rock on the left was the sedimentary rock shale. Now it's the metamorphic rock slate. Slate looks very similar to shale, but harder and more platy. The rock on the right is gneiss. The light and dark minerals have separated into bands. Gneiss is produced by higher temperature metamorphism. The original rock was different in both cases.

Common Metamorphic Rocks

Some of the most common metamorphic rocks are listed below (Table below). Their parent rock and the type of metamorphism are also mentioned.

The table shows some common metamorphic rocks and their original parent rock.

Picture

Rock Name

Type of Metamorphic Rock

CommentsSlate

Foliated

Metamorphism of shalePhyllite

Foliated

Metamorphism of slate, but under greater heat and pressure than slateSchist

Foliated

Often derived from metamorphism of claystone or shale; metamorphosed under more heat and pressure than phylliteGneiss

Foliated

Metamorphism of various different rocks, under extreme conditions of heat and pressureHornfels

Non-foliated

Contact metamorphism of various different rock typesQuartzite

Non-foliated

Metamorphism of quartz sandstoneMarble

Non-foliated

Metamorphism of limestoneMetaconglomerate

Non-foliated

Metamorphism of conglomerate

Summary

Foliated metamorphic rocks are platy.

Non-foliated metamorphic rocks are massive.

The more extreme the amount of metamorphism, the more difficult it is to tell what the original rock was.

Marble is metamorphosed limestone.