3 Mart 2013 Pazar

Idaho State Gemstone

Idaho State Gemstone

Star Garnet

Star garnet is a variety of almandine, a member of the garnet group. Garnets are normally deep red to reddish brown, but other colors exist, including shades of green, yellow, and earth tones. Considered more precious than star sapphires or star rubies, star garnets are usually dark purple or plum. Several varieties of color-changing garnets also exist. The only color garnet does not occur in is blue.
Idaho’s nickname is "The Gem State." Idaho’s mountains contain gold, silver, lead, zinc, cobalt, copper, and many rare minerals, including gems like star garnet, opal, jade, jasper, topaz, zircon, and tourmaline. 
Idaho is the only place in the world, besides India, that has significant deposits of star garnets. Deposits of this stone were found near Fernwood, Idaho, in Benewah County, as early as the 1880s. Today, star garnets are also produced from the placers of Purdue Creek in Latah County, and from an area of the Little North Fork and North Fork of the Clearwater River in Clearwater County, Idaho. The star garnet was designated the official state gem of Idaho in 1967.
Star garnet exhibits a four- or six-pointed star called an asterism, due to inclusions of the mineral rutile. When rutile is densely packed and aligned in a certain way, it will produce the star effect. The word garnet comes 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 name of this stone may also come from the Middle English word gernet meaning "dark red."
Garnet forms from a whole family of minerals, including aluminum, calcium, chromium, silicon, oxygen, magnesium, manganese, iron, and vanadium, into several classifications of garnet.
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 endured.
Star garnet is a relatively rare mineral, occurring only in Idaho and India.
  • India
  • United States: Benewah, Latah, and Clearwater Counties, Idaho
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.
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.
A story in Greek mythology involving Hades and Persephone has led to garnet’s association with gifts that strengthen ties. After Hades abducts Persephone and takes her to the underworld, Zeus sends Hermes to rescue her. As Persephone is leaving, Hades gives her a pomegranate, knowing that once she has experienced the sweetness of the seeds, she will return to him. In fact, Persephone returns to Hades for three months of every year, causing winter on earth. The gift of the pomegranate seeds has been associated with the gift of fine garnet gems.
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
World's Largest Six Ray Star Garnet
Group: Nesosilicates, subgroup Garnet
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
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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