Rock (geology)
- For other uses of "rock", see rock (disambiguation).
A rock is a naturally occurring aggregate of minerals and/or mineraloids. Rocks are classified by mineral and chemical composition, by the texture of the constituent particles and by the processes that formed them. These indicators separate rocks into igneous, sedimentary and metamorphic. They may also be classified according to grain size, in the case of conglomerates and breccias or in the case of individual stones. The Earth's crust (including the lithosphere) and mantle are formed of rock. The transformation of one rock type to another is described by the geological model called the rock cycle.
Petrology is the study of rocks.
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Igneous
Igneous rocks are formed from molten magma and are divided into two main categories: plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallises slowly within the Earth's crust, while volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta. Intrusive igneous rocks usually take a few thousand years to cool whereas extrusive igneous rocks take only a few days or weeks to cool and solidify.
Sedimentary
Sedimentary rocks are formed by deposition of either clastic sediments, organic matter, or chemical precipitates (evaporites), followed by compaction of the particulate matter and cementation during diagenesis. Sedimentary rocks form at or near the Earth's surface.
Metamorphic
Metamorphic rocks are formed by subjecting any rock type (including previously-formed metamorphic rock) to different temperature and pressure conditions than those in which the original rock was formed. These temperatures and pressures are always higher than those at the Earth's surface and must be sufficiently high so as to change the original minerals into other mineral types or else into other forms of the same minerals (e.g. by recrystallisation).
Impact on Society
Rocks have had a huge impact on the cultural and technological advancement of the human race. The mining of rocks for their metal ore content has been one of the most important factors of human advancement. Humanity's advancement has been decided by the kind of metals available from the rocks of a region. The prehistory of civilization is classified into the stone age, iron age, and bronze age. Rocks have been and continue to be used to construct buildings and infrastructure.
See also
- List of minerals
- List of rocks (geological)
- List of stone (building stone)
- Quarrying
- Formation of rocks
- Rock formations (a list of scenic features)
- Megalith (Archaeology)
- Riprap (civil engineering use)
- List of minerals
- Geology
- Geomorphology
References
Categories
Articles lacking sources from December 2006 | All articles lacking sources | Petrology | Materials