Hundreds of minerals have been named after individuals, including a number of gemstones. The gemstones include Hiddenite (W.E. Hidden), Kunzite (George Frederic Kunz), Morganite (J.P. Morgan) and Zoisite (Sigmund Zois).
But there is one gemstone that has the distinction of being the very first mineral ever named after an individual. The gemstone Prehnite was named for its discoverer, Colonel Hendrik von Prehn (1733-1785), a Dutch mineralogist and an early governor of the Cape of Good Hope colony. Prehnite was also the very first mineral to be named and described from South Africa, long before South Africa became an important source for precious gems.
Prehnite is a hydrated calcium aluminum silicate that occurs in a soft yellow-green to apple-green color. Many specimens have an intriguing luminous quality. It has a vitreous to mother-of-pearl luster. Prehnite is a medium-hard gem with a rating of 6 to 6.5 on the Mohs scale. Most prehnite is translucent but transparent specimens are sometimes found. Prehnite has a density or specific gravity of 2.82-2.94 and a refractive index of 1.611-1.669.
Prehnite is usually cut as cabochons or carved. Specimens displaying the cat's-eye effect are known but rare. Recently some green translucent to transparent material has been faceted, producing a new look for prehnite that has become popular for jewelry.
Prehnite can often by found in large sizes, sometimes as large as 100 carats. It is a relatively inexpensive gem, though higher quality faceted material may sell for prices approximately the same as amethyst or citrine. Generally the faceted material is found only in smaller sizes.
Until recently, prehnite was a rare gemstone, but new deposits have made it more available. While you are unlikely to find it in your local jewelry store, gemstone dealers often have some supply. Deposits are found in South Africa, Australia, China, Scotland and the United States.
Prehnite is said to encourages composure, forgiveness and acceptance and is excellent for meditation. Some people also believe that prehnite helps sufferers of claustrophobia.
- First Published: July-03-2008
- Last Updated: October-06-2010
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