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).
Round Faceted Prehnite Gemstone
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 after 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 composed of hydrated calcium aluminum silicate and occurs in a soft yellow-green to apple-green color. Many specimens have an intriguing luminous quality. It has a vitreous to pearly 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 to 2.94 and a refractive index of 1.611 to 1.669.
Oval Checkerboard-Cut Prenite Gemstone
Prehnite is usually cut as cabochons or carved. Specimens displaying the cat's-eye effect are known but rare. Some translucent to transparent material is faceted, producing an interesting look 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 approximating those of 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 supply it. Deposits are found in places including South Africa, Australia, China, Scotland and the United States.
Prehnite is said to encourage composure, forgiveness and acceptance, and is excellent for meditation. Some people also believe that prehnite helps sufferers of claustrophobia.