In geology, rock is a naturally occurring aggregate of minerals and/or mineraloids.
The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three
types, namely, igneous, sedimentary, and metamorphic. The scientific study of rocks is
called petrology, and petrology is an essential component of geology.
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).
Sedimentary rock is one of the three main rock types (the others being igneous and
metamorphic rock). Sedimentary rock is formed by deposition and consolidation of mineral
and organic material and from precipitation of minerals from solution. The processes that
form sedimentary rock occur at the surface of the Earth and within bodies of water. Rock
formed from sediments covers 75-80% of the Earth's land area, and includes common types
such as limestone, chalk, dolostone, sandstone, conglomerate, some types of breccia, and
shale.
Igneous rock (etymology from Latin ignis, fire) is one of the three main rock types (the others
being sedimentary and metamorphic rock). Igneous rocks are formed by solidification of
cooled magma (molten rock). They may form with or without crystallization, either below the
surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This
magma can be derived from partial melts of pre-existing rocks in either the Earth's mantle or
crust. Typically, the melting is caused by one or more of the following processes — an
increase in temperature, a decrease in pressure, or a change in composition. Over 700 types
of igneous rocks have been described, most of them formed beneath the surface of the
Earth's crust. These have diverse properties, depending on their composition and how they
were formed.
A mineral is a naturally occurring solid formed through geological processes that has a
characteristic chemical composition, a highly ordered atomic structure, and specific physical
properties. A rock, by comparison, is an aggregate of minerals and need not have a specific
chemical composition. Minerals range in composition from pure elements and simple salts
to very complex silicates with thousands of known forms.[1] The study of minerals is called
mineralogy.
A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive
mineral, which — when cut and polished — is used to make jewelry or other adornments.[1]
However certain rocks, (such as lapis-lazuli) and organic materials (such as amber or jet)
are not minerals, but are still used for jewelry, and are therefore often considered to be
gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry
because of their lustre or other physical properties that have aesthetic value. Rarity is another
characteristic that lends value to a gemstone.
Source: WikepediA
The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three
types, namely, igneous, sedimentary, and metamorphic. The scientific study of rocks is
called petrology, and petrology is an essential component of geology.
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).
Sedimentary rock is one of the three main rock types (the others being igneous and
metamorphic rock). Sedimentary rock is formed by deposition and consolidation of mineral
and organic material and from precipitation of minerals from solution. The processes that
form sedimentary rock occur at the surface of the Earth and within bodies of water. Rock
formed from sediments covers 75-80% of the Earth's land area, and includes common types
such as limestone, chalk, dolostone, sandstone, conglomerate, some types of breccia, and
shale.
Igneous rock (etymology from Latin ignis, fire) is one of the three main rock types (the others
being sedimentary and metamorphic rock). Igneous rocks are formed by solidification of
cooled magma (molten rock). They may form with or without crystallization, either below the
surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This
magma can be derived from partial melts of pre-existing rocks in either the Earth's mantle or
crust. Typically, the melting is caused by one or more of the following processes — an
increase in temperature, a decrease in pressure, or a change in composition. Over 700 types
of igneous rocks have been described, most of them formed beneath the surface of the
Earth's crust. These have diverse properties, depending on their composition and how they
were formed.
A mineral is a naturally occurring solid formed through geological processes that has a
characteristic chemical composition, a highly ordered atomic structure, and specific physical
properties. A rock, by comparison, is an aggregate of minerals and need not have a specific
chemical composition. Minerals range in composition from pure elements and simple salts
to very complex silicates with thousands of known forms.[1] The study of minerals is called
mineralogy.
A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive
mineral, which — when cut and polished — is used to make jewelry or other adornments.[1]
However certain rocks, (such as lapis-lazuli) and organic materials (such as amber or jet)
are not minerals, but are still used for jewelry, and are therefore often considered to be
gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry
because of their lustre or other physical properties that have aesthetic value. Rarity is another
characteristic that lends value to a gemstone.
Source: WikepediA
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