Metamorphic Stone Types
NATURAL STONE GUIDE—Metamorphic
Metamorphic stone is formed from any pre-existing rock type in the Earth’s crust under variable conditions of high pressures, high temperatures, chemistry, and time. This process produces mechanically deformed stone and chemically altered the mineral assemblages of the parent stone. The new mineral suite may be a different or the same chemical composition as the parent, but as newly formed crystals. Examples of metamorphic rock include: marble, slate, schist, and gneiss (sometimes sold as granite, but technically not).
Metamorphic stones tend to be some of the most beautiful, colorful, and highly figured of any of the dimensional stones. Note that many of the metamorphic stones are up to 3.8 billion (yes, billion) years old.
This of course is a very basic overview of how the various types of stone are formed. There are also exceptions to the rule. Specifically, stone can sometimes be classified as different types.