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Dark inclusions of aegerine in light-green apatite Sketch showing different shapes of inclusions. In mineralogy, an inclusion is any material trapped inside a mineral during its formation. In gemology, it is an object enclosed within a gemstone or reaching its surface from the interior. [1]
This is an accepted version of this page This is the latest accepted revision, reviewed on 10 December 2024. "Skin pigmentation" redirects here. For animal skin pigmentation, see Biological pigment. Extended Coloured family from South Africa showing some spectrum of human skin coloration Human skin color ranges from the darkest brown to the lightest hues. Differences in skin color among ...
A woman with dark skin. Dark skin is a type of human skin color that is rich in melanin pigments. [1] [2] [3] People with dark skin are often referred to as black people, [4] although this usage can be ambiguous in some countries where it is also used to specifically refer to different ethnic groups or populations. [5] [6] [7] [8]
The first modern humans had darker skin as the indigenous people of Africa today. Following migration and settlement in Asia and Europe, the selective pressure dark UV-radiation protecting skin decreased where radiation from the sun was less intense. This resulted in the current range of human skin color.
Hyperpigmentation can be caused by sun damage, inflammation, or other skin injuries, including those related to acne vulgaris. [1] [2] [3]: 854 People with darker skin tones are more prone to hyperpigmentation, especially with excess sun exposure. [4] Many forms of hyperpigmentation are caused by an excess production of melanin. [4]
The timing of mineral crystallization can be used to categorize diamond inclusions into three types: protogenetic, syngenetic, and epigenetic inclusions. [14] Minerals in the protogenetic inclusions were crystallized earlier than the diamond formation. The host diamond encapsulated pre-existing minerals during its crystallization.
The most common mineral inclusion in peridot is the chromium-rich mineral chromite. Magnesium-rich minerals also can exist in the form of pyrope and magnesiochromite. These two types of mineral inclusions are typically surrounded "lily-pad" cleavages. Biotite flakes appear flat, brown, translucent, and tabular. [16]
Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases, [1] [2] is an opaque, [3] impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. The common red color is due to iron(III) inclusions. Jasper breaks with a smooth surface and is used for ornamentation or as ...