Diamond Igneous or Metamorphic

Igneous Rock and Metamorphic Rock

Diamond is a metamorphic mineral, as it forms under heat and pressure from solid-state processes. It forms independently of the igneous rock in which it is found, qualifying it as a type of xenocryst. It is found in an igneous rock is brought to the surface of the earth by volcanic eruptions bringing magma to the surface. It is strictly an allotrope of the element carbon, a mineral, one form of crystal that can be created from carbon.

Igneous rocks are rocks that form from a magma - in other words, they crystallize directly from a liquid. Often these rocks cool slowly and show even, coarse mineral textures such as one sees in granite. At other times they are expelled as volcanic rocks, and "freeze" rapidly into forms that show no discernible crystals, because they have cooled too rapidly for large crystals to form.

In contrast to igneous rocks, formed from liquids, metamorphic rocks form from the heating and pressurization of rock that is already solid. Such raw material can be either igneous, volcanic or sediments. When the solids are reheated and pressurized their mineral constituents react to form a different assemblage of minerals from that found in the original solids. Often there is some water or carbon dioxide present in the metamorphic environment that can serve as additional ingredients in the reaction. Some of the minerals we find in nature are only found in metamorphic environments, and can be used both to identify metamorphic rocks and to estimate the temperatures and pressures at which they were formed.

Metamorphic rocks commonly display relict structures and textures derived from the original rocks. For example, a sedimentary rock deposited in layers may still show layers after metamorphosis, even though the original mineralogy has changed. The preservation of structure is sometimes seen even on a microscopic level - metamorphic minerals can form within the voids left by igneous minerals that have reacted, and may be found presenting distinct crystal shapes that reflect the original minerals rather than the new ones. Thus, even though the chemistry of the rocks changes to reflect the metamorphic environment, the structure of the rocks often retains clues about the materials from which they were originally formed.