January's Garnets

Posted on January 01, 2017 by Tammy Williams

Continuing in our vein of providing birthstone information on a monthly basis, January’s birthstone is garnet. It is also the state mineral of Connecticut, and the gemstone of New York.

The name “garnet” is derived from the Latin “granatum” meaning “pomegranate” because the crystals resemble the red color and seed-like form of this fruit. The garnet is considered by some to symbolize a light heart, loyalty and enduring affection. But to geologists like myself, garnets are known as a group of silicate minerals with a range of hardness from 6.5 to 7.5 - and sometimes higher - on the Mohs scale of hardness. Unlike many gemstones, the garnet is not just one mineral, but has many different chemical compositions, which accounts for the reason it comes in such a wide range of colors including red, orange, yellow, green, purple, brown, blue, black, pink, and colorless, with reddish shades most common.  Geologists also use the garnet group as a key mineral in defining the genesis of metamorphic and igneous rocks. Each variety is found to occur within certain temperature ranges and as such when found in a rock formation it can help to determine the temperature / time of the rocks surrounding it were formed. Garnets are commonly found as small pebbles in streams, where the igneous and metamorphic rocks that contain them have weathered away. They are also found intact as part of metamorphic or igneous rock facies.  They’re found in many places around the world, including North and South America, Australia, India, Asia and Spain.

Garnets have been used since the Bronze age as both jewelry and abrasives. In the former Czechoslovakia, evidence of garnet jewelry dating to the Bronze age was found in ancient graves in the former Czechoslovakia. Garnet jewelry has also been discovered dating back to 3100 B.C. in Egypt, 2300 B.C. in Sumeria, and 2000-1000 B.C. in Sweden. Red garnets were the most commonly used gemstones in the Late Antique Roman world, and the Migration Period art of the "barbarian" peoples who took over the territory of the Western Roman Empire. They were especially used in the cloisonné (inlaid in gold) technique, a style often just called garnet cloisonné, found from Anglo-Saxon England, like that of pieces found as part of the Staffordshire horde discovered in 2009. Pre-Columbian Aztec and Native Americans also used garnets in their ornaments. Besides being used as jewelry, ancient warriors believed that garnets brought victory and the Crusaders used them for protection. Asiatic warriors believed that glowing garnets, used as bullets, inflicted more severe wounds. In 1892, during hostilities on the Kashmir frontier, the Hanza tribesmen fired on British soldiers with garnet bullets, believing them to be more effective than lead bullets. Garnet is still used today for both jewelry and as an abrasive, such as that found in sandpaper.

Although there is only one gemstone for the month of January, as mentioned there are many varieties of Garnet, a few of which are described further in this article. One of the most common garnets is Almandine sometimes called almandite or almandine ruby. The name Almandine is a corruption of the world Alabanda, from an Asia Minor region where stones were cut in ancient times. The deep red transparent color of this iron/aluminum-rich garnet make it one of the most commonly used of the gem garnets and occurs in metamorphic rocks like mica schists.

Andradite garnet has a variable composition and as such it may be found as red, yellow, green or black. Demantoid (green) is a particular favorite variety of Andradite and has been called the “emerald of the Urals” and is one of the most sought after garnet varieties.

Grossular garnet is a fairly common variety where the name is derived from the botanical name for gooseberry, grossularia, in reference to the green garnet that is found in Siberia. There are other shades of grossular though that include cinnamon brown, red, and yellow. The grossular garnet from Kenya and Tanzania is called tsavorite for the Tsavo area of Kenya.

Pyrope (from the Greek pyrōpós meaning "fire-eyed") is red in color and chemically a magnesium aluminum silicate, though the magnesium can be replaced in part by calcium and ferrous iron. The color of pyrope varies from deep red to black. A beautiful orange variety of garnet, Spessartine, is found in Madagascar, while violet-red varieties, sometimes called rhodolite (Greek for “rose”) are found in Colorado and Maine. Blue Pyrope-Spessartine garnets discovered in Madagascar, parts of the United States, Russia, Kenya, Tanzania and Turkey, change color from blue-green to purple depending on the color temperature of the viewing light. The color change is due to the high amount of vanadium in the garnets. This is the rarest type of garnet. Pyrope has many tradenames: California Ruby, Rocky Mountain Ruby, Arizona Ruby, Cape Ruby, and Bohemian Garnet.

Finally, Ubarovite is a rare garnet, a very bright green in color usually found in the Ural mountains of Russia and Finland.

 Grossular GarnetDemantoid GarnetFaceted Garnet Ring

 

Posted in Garnet, January


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