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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 ]
The aluminium-bearing minerals of these fragments provide clues to the depth of origin. Calcic plagioclase is stable to a depth of 25 km (16 mi). Between 25 km (16 mi) and about 60 km (37 mi), spinel is the stable aluminium phase. At depths greater than about 60 km, dense garnet becomes the aluminium-bearing
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]
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.
Peridotite, a type of ultramafic rock. Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are usually composed of greater than 90% mafic minerals (dark colored, high magnesium and iron content).
They are usually dark in color, owing to the abundance of ferro-magnesian silicates, of high specific gravity and liable to decomposition. For these reasons they have been defined as a melanocrate series (rich in the dark minerals ); and they are often accompanied by a complementary leucocrate series (rich in the white minerals feldspar and ...
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Diamond crystals in a diamond can also be present in the form of long and thin needles. These may not be visible to the naked eye, unless the needle inclusion is of a noticeable color or has a noticeable presence. Some needle inclusions are also known to give diamonds a special look.