Amphibolite is a non-foliated metamorphic rock that forms through recrystallization under conditions of high viscosity and directed pressure. It is composed primarily of hornblende (amphibole) and plagioclase, usually with very little quartz. The specimen shown above is about two inches (five centimeters) across.
What are Metamorphic Rocks?
Metamorphic rocks have been modified by heat, pressure, and chemical processes, usually while buried deep below Earth's surface. Exposure to these extreme conditions has altered the mineralogy, texture, and chemical composition of the rocks.
There are two basic types of metamorphic rocks. Foliated metamorphic rocks such as gneiss, phyllite, schist, and slate have a layered or banded appearance that is produced by exposure to heat and directed pressure.
Non-foliated metamorphic rocks such as hornfels, marble, quartzite, and novaculite do not have a layered or banded appearance. Pictures and brief descriptions of some common types of metamorphic rocks are shown on this page.
The best way to learn about rocks is to have a collection of specimens to examine while you study. Seeing and handling the rocks will help you understand their composition and texture much better than reading about them on a website or in a book. The Geology.com store offers inexpensive rock collections that can be mailed anywhere in the United States or U.S. Territories. Mineral collections and instructive books are also available.
Soapstone is a metamorphic rock that consists primarily of talc with varying amounts of other minerals such as micas, chlorite, amphiboles, pyroxenes, and carbonates. It is a soft, dense, heat-resistant rock that has a high specific heat capacity. These properties make it useful for a wide variety of architectural, practical, and artistic uses.
Author: Hobart M. King, Ph.D.