Garnet
Garnet, the birthstone for January, received its nomenclature from the Latin plagiaristic word granatus, which explains - like a grain, which dates to the form of incidence wherein crystals look a lot like grains or seeds implanted in the matrix. Garnet is a kin of minerals possessing analogous corporeal and crystalline properties.
There are a number of trades and array of names offered to refer for garnet, most of these nomenclatures are for meticulous colors of a species. Hessonite is the assortment name for a superior orange, cinnamon brown or pinkish range of grossularite, while tsavorite is the commercial name given for the superior dark green grossularite. Melanite is a black titanium demeanor variant of andradite and demantoid is a wealthy green type. Malaya is a commercial name for a pyrope-spessartite that ranges in color from red, through varying shades of orange and brownish orange to peach and pink.
Uses of Garnets :
Pure crystals of garnet are used as gemstones. Garnet sand is a good abrasive, and a common replacement for silica sand in sand blasting. Mixed with very high pressure water, garnet is used to cut steel and other materials in water jets. Garnet sand is also used for water filtration media.
* In the USA it is known as the birthstone for January.
* It is the gemstone for the 2nd wedding anniversary .
* It is the state mineral of Connecticut.
* It is also New York's gemstone.
Geological importance of Garnet :
The Garnet group is a key mineral in interpreting the genesis of many igneous and metamorphic rocks via geothermobarometry. Diffusion of elements is relatively slow in garnet compared to rates in many other minerals, and garnets are also relatively resistant to alteration. Hence, individual garnets commonly preserve compositional zonations that are used to interpret the temperature-time histories of the rocks in which they grew. Garnet grains that lack compositional zonation commonly are interpreted as having been homogenized by diffusion, and the inferred homogenization also has implications for the temperature-time history of the host rock.
Garnets are also useful in defining metamorphic facies of rocks. For instance, eclogite can be defined as a rock of basalt composition, but mainly consisting of garnet and omphacite. Pyrope-rich garnet is restricted to relatively high-pressure metamorphic rocks, such as those in the lower crust and in the Earth's mantle. Peridotite may contain plagioclase, or aluminium-rich spinel, or pyrope-rich garnet, and the presence of each of the three minerals defines a pressure-temperature range in which the mineral could equilibrate with olivine plus pyroxene: the three are listed in order of increasing pressure for stability of the peridotite mineral assemblage. Hence, garnet peridotite must have been formed at great depth in the earth. Xenoliths of garnet peridotite have been carried up from depths of 100 km and greater by kimberlite, and garnets from such disaggegated xenoliths are used as a kimberlite indicator minerals in diamond prospecting. At depths of about 300 to 400 km and greater, a pyroxene component is dissolved in garnet, by the substitution of (Mg,Fe) plus Si for 2Al in the octahedral (Y) site in the garnet structure, creating unusually silica-rich garnets that have solid solution towards majorite. Such silica-rich garnets have been identified as inclusions within diamonds.
