 Courtesy of GIA Educational Images © Gemological Institute of America. |
GO 340 Gemstones & Gemology
academic.emporia.edu/abersusa/go340/garnet.htm
|  Courtesy of GIA Educational Images © Gemological Institute of America. |
Courtesy of GIA Educational Images © Gemological Institute of America. |
GO 340 Gemstones & Gemology
academic.emporia.edu/abersusa/go340/garnet.htm
| Courtesy of GIA Educational Images © Gemological Institute of America. |
 Spessartite Garnet. Courtesy of GIA Educational Images © Gemological Institute of America. |
Garnet is a group name that comprises minerals with common crystal structure but different chemical compositions. The main species names are pyrope, almandine, spessartine, grossular, andradite, and uvarovite. The data common to all garnet is a hardness of 6.5-7.5, and a conchoidal to splintery fracture, brittle tenacity. Garnet's crystal system is isometric which is reflected in the common dodecahedral crystal form. It ranges from transparent to opaque, with a vitreous luster. Garnet is singly refractive, with a refractive index associated with each variety, ranging from 1.72-1.756. Garnet often exhibits anomalous douby refraction. There is no pleochroism or little to weak fluorescence. The specific gravity is different with each variety, but all will sink in the highest specific gravity heavy liquid, 3.32. |
| It used to be common knowledge that garnet came in every color of the rainbow except blue. This is no longer true! Garnet does come in blue and is a color changing stone with a similar phenomenon as alexandrite. Richard Wise wrote on Madagascar Blue Color-Change Garnet, which can be found at http://www.secretsofthegemtrade.com/articles_8.htm. This is an excerpt from his new book, Secrets of the Gem Trade. (This is also available at his newer website, www.rwwise.com/mbeg.html.)
Almandine and pyrope are the best known garnets used as gemstones. Pyrope, a red garnet with a brown tint, has a specific gravity (SG) of 3.62-3.87 and refractive index (RI) range between 1.72 and 1.756. It was the Bohemian |
 Pyrope Garnet. Image taken from Gem Hut. |
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Almandine, a red garnet with violet tint, has a SG of 3.93-4.3 and RI range from 1.77 to 1.82.
Andradite, a black, brown, yellow- and orange-brown garnet, has a SG of 3.7-4.1 and RI range 1.88 to 1.94. Spessartine, an orange to red-brown garnet, has a SG of 4.12-4.18 and RI range from 1.79-1.82. <<< Almandite Garnet is the image to the left. Image was taken from Gem Hut.
Image right is a variety of faceted garnets displaying the range of colors.>>> |
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| Tsavorite (tsavolite) is a deep green variety of grossular garnet. Grossular, a colorless, white, yellow, yellowish green, dark green, and
brown garnet, has a SG of 3.57-3.73 and RI range of 1.734 to 1.759. This garnet was found in gem quality for the first time in 1978 and includes a variety names such as demantoid (most valuable garnet, green to emerald green), melanite (black, found in mourning
jewelry), and topazolite (yellow). Demantoid is often confused with grossular and uvarovite garnets, as well as peridot, emerald, spinel,and tourmaline. Uvarovite, a emerald green garnet, has a SG of 3.41-3.52 and RI of 1.87. Uvarovite is rarely gem quality and often confused with demantoid and emerald.
A must read is Richard Wise on Tsavorite: King of African Gems (http://www.secretsofthegemtrade.com/articles_12.htm), |
 Tsavorite Garnet. Image taken from Gem Hut. |
 Tsavorite Garnet. Image courtesy of GIA Educational Images © Gemological Institute of America. |  Horsetail inclusions in demantoid garnet. Image courtesy of GIA Educational Images © Gemological Institute of America. |
Malaya Garnet. courtesy of GIA Educational Images © Gemological Institute of America. |
Garnet is the birthstone for January and the second year anniversary gem. In addition to garnet variety names, gem trade names include hessonite, malay, rhodolite, and almandite to name a few (Jewelry Central). Hessonite is a cinnamon orange type of grossular garnet, while Malay is a trade name for pyrope-almandine-spessartine-grossular-andradite garnet with a range of colors from orangish brown to peachy pink.
Read Richard Wise on Luck Be A Lady Tonight - The Discovery of Malaya Garnet, http://www.secretsofthegemtrade.com/articles_7.htm, an excerpt from
Secrets of the Gem Trade. |
Malaya Garnet. Image taken from GIS Educational Images © Gemological Institute of America. |
| Rhodolite is purplish red pyrope-almandine garnet and almandite refers to almandine-pyrope solid solution garnets that are often used as abrasives in industry. A beautiful gem quality, intensely colored, purple-red garnet exists as well, and is referred to as Grape Garnet. This is a trade marked name by Columia Gem House, Inc. and Fair Trade Gems, online at www.columbiagemhouse.com/ and www.columbiagemhouse.com/fairtradegems.html, as well as Trigem Designs, www.trigemdesigns.com/home/. Trigem Designs website describes color of Grape Garnet as having the glow of a fine merlot wine (www.trigemdesigns.com/gems/purple-gems.php), and stated that this garnet comes from the Bay of Bengal, eastern India. |  Rhodolite (Pyrope-Almandine). Image taken from Gem Hut. |
| For gem garnet information, including the history and lore, visit CW Jewelers. Also, a beautiful pyrope garnet Victorian hairpiece can be found at http://www.mnh.si.edu/earth/text/2_2_3_3.html, a Smithsonian site (if this webpage address does not work, go to http://www.mnh.si.edu/earth/text/index.html The Dynamic Earth and follow links from Gems and Minerals, Mineral Color, and Garnet's Many Colors.
<<< Image left, rhodolite garnets taken from GIS Educational Images © Gemological Institute of America. |
Return to the Syllabus or choose another gemstone below.
| Alexandrite | Amber | Amethyst | Chalcedony | Diamond | Emerald |
| Garnet | Jade | Malachite | Opal | Pearl | Peridot |
| Ruby | Sapphire | Tanzanite | Topaz | Tourmaline | Turquoise |
This page originates from the Earth Science department for the use and benefit of students enrolled at Emporia State University. For more information contact the course instructor, S. W. Aber, e-mail: esu.abersusie@gmail.com Thanks for visiting! Webpage created: November 15, 2000; last update: September 21, 2011.
Copyright 1999-2011 Susan Ward Aber. All rights reserved.