Folds in a metamorphic rock

Rocks are formed from minerals and can be divided into three general types.

Sedimentary: A rock that is formed at or near the Earth's surface from either deposits formed by the products of erosion and weathering (such as sand and clay), or from organic debris (eg shells or plants), or from the solid salts left behind when water evaporates. Sedimentary rocks often have a layered appearance. Examples: Sandstone and limestone.

Metamorphic: Any rock that is altered by high temperatures and pressures, but has not melted. Metamorphic rocks often have a wavy, deformed appearance. Examples: Marble and schist.

Igneous: A rock that forms from molten magma. Igneous rocks are crystalline and can form either within the Earth's crust or, if they are erupted from a volcano, at the Earth's surface. Examples: granite and basalt.

Image: Folds in a metamorphic rock (credit: Herve Conge, ISM/SPL)

Introduction

Folds in a metamorphic rock Rocks

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Rocks

In geology, a rock is a naturally occurring solid aggregate of one or more minerals or mineraloids. For example, the common rock granite is a combination of the quartz, feldspar and biotite minerals. The Earth's outer solid layer, the lithosphere, is made of rock.

Rocks have been used by mankind throughout history. From the Stone Age rocks have been used for tools. The minerals and metals we find in rocks have been essential to human civilization.

Three major groups of rocks are defined: igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is an essential component of geology.

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