The Wonderful Gemstone
Garnet
by Scott Chilcutt

Garnet,  Latin for like seeds, is a gemstone that occurs in many colors, except blue. It has a vitreous luster, a white streak, and is normally transparent to translucent. On Moh's hardness scale, garnet has a hardness between 6.5 to 7.5. The specific gravity varies between 3.56 and 4.32, depending upon the chemical composition. The garnet group of minerals have many different chemical formulas. Garnets do not have good cleavage, and they fracture just like quartz, conchoidal or uneven. Garnet is a mineral in the isometric (cubic) crystal system, and is often found in dodecahedrons or trapezohedrons.

There are many interesting beliefs and mystic stories recorded about garnets. Garnet may even protect one from thieves. Normally garnets were exchanged between friends to ensure that they would meet again and to symbolize their affection. Garnets were supposed to hold healing properties, relieving skin conditions, protecting against poisons, and if placed under the pillow, garnet would protect one from bad dreams. Magical properties were assigned in the 13th century when garnet was used in rituals. It was suspose to repel insects and some five hundred years ago, people believed that it would drive away demons.



Pyrope Garnet
Pyrope, Greek for fiery, was the stone of the 18th and 19th centuries (Schumann, 1997). Pyrope is deep red to reddish black in color. Its chemical composition is Mg3Al2(SiO4)3. The best place to collect pyrope is from peridotites containing olivine and hypersthene. Pyrope mining occurs in Burma, China, Madagascar, Sri Lanka, South Africa, Tanzania, and within the US, Kentucky, Arkansas, Arizona, New Mexico, and Utah.


Almandine Garnet

Named for a small town in Asia Minor, almandine garnet occurs in dioritic rock, with andalusite, hornblende, and biotite, in hornfels, and schists of contact and regional metamorphism. Almandine is red to brown, or brownish black, in color. The chemical formula is Fe3Al2(SiO4)3. It is mined in Brazil, India, Madagascar, Sri Lanka, the Czech Republic, and Austria. The best place to locate almandine in the US, is in Alaska, Idaho, and Michigan.


Spessartine is German for forest, and has a brownish red to hyacinth red color. It is found with albite and muscovite in granite pegmatites, and with quartz and riebeckite in blue schist. Spessartine is composed of Mn3Al2(SiO4)3. It is mined in Germany, Burma, Brazil, China, Kenya, Madagascar, Sri Lanka, and Tanzania. In the US, this garnet is found in Virginia, California, Nevada, and Colorado.
Spessartine Garnet



Grossular Garnet
Grossular garnets come in a variety of differing colors, browns, reds, colorless, green (opaque to a brilliant emerald shade), and black. These colors are due to the replacement of the Al3+ in some of the molecules by other elements. The main chemical composition is Ca3Al2(SiO4)3. These types of garnets form with wollastonite, calcite, and vesuvianite in hornfels of contact metamorphic rocks. They are found in Canada, Kenya, Mali, Pakistan, Russia, Sri Lanka, South Africa, and Tanzania. Grossular garnets are mined in Maine and Vermont in the US.

Variety names within grossular garnets include hessonite (red/brown), leuco garnet (colorless), Hydorgrossular (opaque green), and tsavolite/tsavorite (emerald green). The yellow has still not been named or has been named after the date in which the material for this web page was printed. Grossular is Greek for gooseberry.



Andradite Garnet

Andradite comes in a variety of colors, wine red, greenish, yellow, brown, and black. These types of garnets are found with albite and biotite in granite pegmatites, with orthoclase, calcite, and wollastonite in carbonatites, with calcite and hedenbergite in hornfels of contact metamorphic rocks, and with magnetite and hedenbergite in skarn of hydrothermal metamorphic rocks. Andradite has the chemical formula Ca3Fe2(SiO4)3. These garnets are mined in China, Korea, Russia, Zaire, Germany, France, Italy, and Switzerland. Within the US, andradite can be found in New Jersey, California, Pennsylvania, and Arizona. There are varieties of andradite that include, demantoid (green), which is the most valuable of all garnets, melanite (opaque, black), and topazolite (yellow). The name andradite comes from a Portuguese mineralogist.



Uvarovite is emerald green in color, and was named for a Russian statesman. It has the chemical composition Ca3Cr2(SiO4)3. It occurs with olivine and chromite in peridotite and in serpentine of hydrothermal metamorphic rocks. This type of garnet is mined in Finland, India, Canada, Poland, Russia (Urals). In the US it is found only in California.
Uvarovite Garnet


References

Images:

Chesterman, C. W. (1993). The Audubon Society Field Guide to North American Rocks and Minerals 11th edition. Colored plates scanned include minerals contained on pages 3, 4, 10, 146, 175, 176, 177, 223, 239, 240, 309, 311, 363, 507, 512.

Text:

Chesterman, C. W. (1993). The Audubon Society Field Guide to North American Rocks and Minerals 11th edition, pg. 582-586

Schumann, W. (1997). Gemstones of the World, p. 104-106.

Wiehe, Christine, Personal Contact.

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