For the geologist, the term rock means a natural aggregate mineral of resources, which may include some organic solids such as fossils or glass. Rocks are generally divided into three main classes: igneous, sedimentary and metamorphic. These classes are related to a common origin or genesis. Volcanic rocks formed during cooling of the liquid rock and related volcanic eruptive processes. Sedimentary rocks are formed by the compaction and cementation of sediments. Metamorphic rocks are developed due to the solid body of chemical and physical changes in pre-existing rocks due to the rise in temperature, pressure or chemically active liquids.
Rock is extremely common in the earth’s crust, igneous rocks of volcanic origin form the molten material.
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