Types of Rocks
Three Basic Rock Types. The earth’s crust is composed of three basic rock types: igneous, sedimentary and metamorphic. Igneous rocks. Igneous Rocks are formed from the crystallization of molten rock (magma or lava) from within the earth’s mantle. Common igneous rocks include granite, basalt, and gabbros. Metamorphic rocks. Metamorphic Rocks are formed from pre-existing rocks by mineralogical, chemical and/or structural changes in response to marked changes in temperature, pressure, shearing stress, and chemical environment. These changes generally take place deep within the earth’s crust. Examples of common metamorphic rocks include slate, marble and schist. Sedimentary rocks. Sedimentary Rocks are formed as sediments, either from eroded fragments of older rocks or chemical precipitates. Sediments lithify by both compaction, as the grains are squeezed ...