Facts about Garnet
Garnet is a key mineral in interpreting the genesis of many igneous and metamorphic rocks via geothermobarometry.
Chemically, almandite is an iron-aluminum garnet with the formula Fe3Al2(SiO4)3; the deep red transparent stones are often called precious garnet and are used as gemstones (being the most common of the gem garnets).
The rarest of these is the blue garnet, discovered in the late 1990s in Bekily, Madagascar.
Garnets do not show cleavage, so when they fracture under stress, sharp irregular pieces are formed.
Garnet sand is a good abrasive, and a common replacement for silica sand in sand blasting.
Garnets are most often found in the dodecahedral crystal habit, but are also commonly found in the trapezohedron habit.
The garnets from mantle derived rocks, peridotites and eclogites, commonly contain a pyrope variety.
Hence, individual garnets commonly preserve compositional zonations that are used to interpret the temperature-time histories of the rocks in which they grew.
When doped with neodymium (Nd3+), these YAl-Garnets are useful as the lasing medium in lasers.
Mixed with very high pressure water, garnet is used to cut steel and other materials in water jets.
Grossular is a calcium-aluminum garnet with the formula Ca3Al2(SiO4)3, though the calcium may in part be replaced by ferrous iron and the aluminum by ferric iron.
Garnets are found in many colors including red, orange, yellow, green, blue, purple, brown, black, pink and colorless.
The garnets make up two solid solution series: pyrope-almandine-spessarite and uvarovite-grossular-andradite.
Knorringite is a magnesium chromium garnet species with the formula Mg3Cr2(SiO4)3.
The name grossular is derived from the botanical name for the gooseberry, grossularia, in reference to the green garnet of this composition that is found in Siberia.
Spessartite of a beautiful orange-yellow is found in Madagascar (see Mandarin garnet).
In yttrium iron garnet (YIG), Y3Fe2(FeO4)3, the five iron(III) ions occupy two octahedral and three tetrahedral sites, with the yttrium(III) ions coordinated by eight oxygen ions in an irregular cube.
Almandite has nicknames of Oriental garnet, almandine ruby, and carbuncle.
Garnet’s light transmission properties can range from the gemstone-quality transparent specimens to the opaque varieties used for industrial purposes as abrasives.
One of the most sought after varieties of gem garnet is the fine green grossular garnet from Kenya and Tanzania called tsavorite.
Pyrope has tradenames some of which are misnomers; Cape ruby, Arizona ruby, California ruby, Rocky Mountain ruby, and Bohemian garnet from the Czech Republic.
Yttrium aluminium garnet (YAG), Y3Al2(AlO4)3, is used for synthetic gemstones.
Andradite is a calcium-iron garnet, Ca3Fe2(SiO4)3, is of variable composition and may be red, yellow, brown, green or black.
Another intriguing find is the blue color-change garnets from Madagascar, a pyrope spessartine mix.
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.
Six common varieties of garnet are recognized based on their chemical composition.
Garnets are most often seen in red, but are available in a wide variety of colors spanning the entire spectrum.
One example for this is gadolinium gallium garnet, Gd3Ga2(GaO4)3, which is synthesized for use in magnetic bubble memory.
Demantoid has been called the "emerald of the Urals" from its occurrence there, and is one of the most prized of garnet varieties.
Xenoliths of garnet peridotite have been carried up from depths of 100 kilometers and greater by kimberlite, and garnets from such disaggregated xenoliths are used as a kimberlite indicator minerals in diamond prospecting.
Very high pressure streams of garnet sand mixed into water (Water jets) are used to cut steel and other materials.
Garnet is a group of minerals that have been used since the Bronze Age as gemstones and abrasives.
Diffusion of elements is relatively slow in garnet compared to rates in many other minerals, and garnets are also relatively resistant to alteration.
Pyrope-rich garnet is restricted to relatively high-pressure metamorphic rocks, such as those in the lower crust and in the Earth's mantle.
Though both rubies and garnets are beautiful red stones, you really don't want to confuse the two. Specifically, you don't want to pay for a ruby and wear a garnet. At a brief glance, they look very similar. However, rubies are considered one of the most valuable gemstones whereas garnets are, well, not.Mar 30, 2015
The variety Rhodolite has become a very important jewelry gemstone, and the rare green Tsavorite and Demantoid Garnets make exquisite and costly gemstones. Color Changing Garnet has sparked recent interest, and it is most often used in rings.
Almandine is the variety of garnet that is most often used in industry. Garnet abrasive: This photo shows garnet granules that have been crushed and size-graded for use as abrasive, cutting, and filter media. They are used in waterjet cutting, "sand" blasting, sandpaper, water filtration, and a number of other uses.