12 Mayıs 2013 Pazar

Vermont State Gemstone

Vermont State Gemstone

Grossular Garnet

Taken as a whole, the garnet group, comprising several chemically and physically similar members, is one of the more common minerals. Some members, however, are quite rare and are prized by collectors and for use as gems. Garnets are normally deep red to reddish brown, but can also be brown, black, green, yellow, orange, pink, white, or colorless. Several varieties of color-changing garnets also exist. Grossular, also known as grossularite, is the calcium aluminum garnet; it forms in contact with metamorphosed calcareous rocks. Grossular has many color possibilities and is probably the most colorful of the garnets. The orange variety is the most common.
The main members of the garnet group are pyrope, almandine, spessartine, grossular, andradite, and uvarovite. Hessonite is the variety name for a fine orange, cinnamon brown, or pinkish variety of grossularite, while tsavorite is the trade name for fine dark green grossularite. Melanite is a black titanium-bearing variety of andradite, and demantoid is a rich green variety. Rhodolite is a purplish-red, pyrope-almandite, solid-solution garnet. All species of garnet occur as gemstone quality.
The only color garnet does not occur in is blue.
Grossular garnet from the Mt. Belvidere Quarries at Lowell and Eden, Vermont, is thought to be the finest of its kind anywhere. Vermont designated grossular garnet as the official state gem in 1991.
The word garnet may come from the Latin words granatus or granum, which mean "grain" or "grainy," and refer to the stone’s formation, wherein crystals resemble grains or seeds embedded in the matrix. The Latin word granatium means "pomegranate." The name of this stone may also come from the Middle English word gernet, meaning "dark red." Grossular garnet forms rounded crystals, and its name comes from the Latin grossularia meaning, "gooseberry."
Garnets form under the high temperatures and/or pressures that metamorphic and igneous rocks must endure. Geologists use garnets as a gauge of how much temperature and pressure a rock has experienced.
Garnet forms from a whole family of minerals, including aluminum, calcium, chromium, silicon, oxygen, magnesium, manganese, iron, and vanadium, into several classifications of garnet. Grossular is one of the main members of the garnet group, along with pyrope, almandine, spessartine, andradite, and uvarovite.
The green variety of grossular garnet is called tsavorite, which is occasionally cut as a gem. Hessonite is the name for an orange, cinnamon brown, red, or pinkish variety of grossularite, while tsavorite is the trade name for fine, dark green grossularite.
Garnet is found throughout the world. Grossular garnet is found in the following localities:
  • Russia: near Chernyshevsk, at the confluence of the Vilyui and Akhtaragda Rivers, Yakutia
  • Italy: Ala Valley, Piedmont
  • Austria: Zillertal, Tirol
  • Romania: Ocna de Fier
  • Canada: Jerrey mine, Asbestos, Quebec
  • USA: Standish, Cumberland County, Maine; Belvidere Mountain quarries, Lowell, Orleans County, Vermont; Crestmore, Riverside County, California; the Old Cosumnes copper mine, El Dorado County, California; San Carlos mine, Mazourka Canyon, Inyo Range, Inyo County, California; Santa Rosa, Sonoma County, California; and Vesper Peak, Sultan Basin, Snohomish County, Washington
  • Mexico, Xalostoc and Morelos, Chihuahua and Sierra de la Cruces, near Lake Jaco, Coahuila
  • Tanzania: Merelani Hills, southeast of Arusha
  • Kenya: Taita Hills, near Voi
Historical Uses
Humans have used and worn garnet for thousands of years. It is said that Noah used a garnet lantern to help him light the way while steering the ark. This may have led explorers and travelers to carry the stone to light their way and protect them from disaster. Early Egyptians, Greeks, and Romans used garnet in jewelry.
Modern Uses
A very small number of garnets are flawless enough to be cut as gemstones. To display the star effect, a garnet must be cut as a cabochon. Star gemstones tend to be opaque rather than transparent due to the presence of the inclusions.
The majority of garnet mining is for massive garnet that is crushed and used to make abrasives. Harder garnets are also used to make garnet paper, a type of sandpaper.
In 1994, United States production of industrial garnet was valued at about $14 million, while gem garnet production was valued at only about $233,000. According to the U.S. Geological Survey, U.S. production of gem-grade garnet will continue to increase and additional deposits will be brought into use in the coming years.
Garnet’s powers are believed to include healing, strength, and protection. It has been said that garnet gifts demonstrate affection for friends and lovers, strengthen bonds and heal broken ones, and help to insure that the pair will meet again. The stone is also believed to regulate the heart and blood flow, relieve inflammation, maintain sleep, and aid in curing depression.
Garnet is the traditional and modern birthstone for those born in January. It is also the stone for the Zodiac sign Aquarius, and may be given as a gem on the second and sixth wedding anniversary.
State Gemstone
Grossular Garnet
State Gemstone
Grossular Garnet Gem
State Gemstone
Close-up of Grossular Garnet
Group: Nesosilicates
Chemical Formula:  (Ca2+, Mg2+, Fe2+)3(Al3+, Fe3+, Cr3+)2(SiO4)3
Crystal Structure: Cubic
Hardness (Mohs): 6.0-7.5
Color: Virtually all colors except blue
Transparency: Transparent
Luster: Pyrope, almandine, spessartine, and grossular have a vitreous luster. Andradite (including demantoid) and uvarovite have an adamantine luster.
Birefringence: None
Pleochroism: None
Refractive Index: 1.72-1.94
Density: 3.60-3.80
Streak: White
Cleavage: Imperfect
Fracture: Conchoidal to uneven

Some data courtesy of the Mineralogical Society of America
Author: World Trade Press

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