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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 ] According to James Hutton 's law of inclusions, fragments included in a host rock are older than the host rock itself.
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 ...
Hydrothermal ore minerals, which typically form from high temperature aqueous solutions, trap tiny bubbles of liquids or gases when cooling and forming solid rock. The trapped fluid in an inclusion preserves a record of the composition, temperature and pressure of the mineralizing environment. [1] An inclusion often contains two or more phases ...
A reaction rim (light grey area) is formed around the host mineral (dark grey) when the temperature and pressure decrease. symplectites: Intergrowth of fayalite-pyroxene symplectite (grey) against apatite (white) exhibits a symplectitic texture on the right. cross-cutting
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).
When a rock undergoes partial melting some minerals will melt (neosome, i.e. newly formed), while others remain solid (paleosome, i.e. older formation). The neosome is composed of lightly colored areas (leucosome) and dark areas (melanosome). The leucosome lies in the center of the layers and is mainly composed of quartz and feldspar.
Melt inclusions are generally small - most are less than 80 micrometres across (a micrometre is one thousandth of a millimeter, or about 0.00004 inches). [4] They may contain a number of different constituents, including glass (which represents melt that has been quenched by rapid cooling), small crystals and a separate vapour-rich bubble. [5]