Garnet got its name from the Latin word "granatus," meaning grain and is a January birthstone. It is a common misconception that garnets only come in one variety (deep red stones). The word garnet actually represents more than 10 different gemstones of similar chemical composition and a spectrum of hues. Furthermore, garnets have a hardness between 7 and 7.5 on the Mohs scale and have a relatively high index of refraction.
Examples
Garnet is in a family of minerals that have the same general chemical formula, according to the U.S. Geological Survey (USGS), along with similar crystalline and physical properties. The most common types of garnet are uvarovite, pyrope, grossularite, almandite, spssartite and anderadite. Other types varieties, or species, include hessonite (named for its orange color), grossularite (named for its dark green pigment) and melanite.
The Facts
Garnets come in a variety of colors except blue. For example, andradite garnet can be green, greenish brown, greenish yellow, orange yellow, gray or black, according to the USGS. Some garnets are even able to change color, meaning that they are one color when observed in natural light and another when observed under incandescent light.
History
While garnet has a long history as a gemstone (back to pre-history), its use in industry can only be traced back to 1878, according to the USGS. Henry Hudson Barton, the founder of the Barton Mines Corporation, was the first to use garnets in industry when he used them to make garnet coated sandpaper. Since then, garnet has seen a huge increase in industrial use (up to about 110,000 tons per year) and, in 1994, the production of garnet in United States was approximated at about $14 million. In perspective, gem garnet production is approximated to be at about $233,000.
Structure
Garnet is made up of three calcium, two aluminum, three silicon and 12 oxygen atoms. The oxygen atoms are bonded to two calcium, one aluminum and one silicon atom. The silicon atoms are bonded to four oxygen atoms (called tetrahedra). The aluminum atoms are bonded to six oxygen atoms (called octahedra) and the calcium atoms are bonded to eight oxygen atoms (called a distorted cube).
Location
Garnet is found in many areas of United States. These include Alaska (along the Stikine River), Arizona (in Apache County and near the New Mexico border), California (in El Dorado, Fresno, Orange, and San Diego Counties), Colorado (near Nathrop County), Connecticut (near Roxbury Falls), Idaho (near Fernwood and Benewa Counties), Montana, Nevada, New Hampshire, New York, North Carolina, Pennsylvania, Utah and Virginia.
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