A number of gemstones were first discovered in the United States. The most famous ones include:

» Hiddenite: the green form of spodumene, in North Carolina

» Bixbite: the rare form of red beryl, in southwestern Utah

» Kunzite, the pink form of spodumene, in San Diego County, California

» Unakite: granitic rock, in the Unakas Mountains of North Carolina

» Morganite, pink form of beryl, in San Diego County, California

» Benitoite: rare blue barium titanium silicate, in San Benito County, California

Faceted Danburite

One of the less well known gemstones first discovered in the USA is Danburite, a calcium boric silicate first discovered in 1839 in Danbury, Connecticut. The city of Danbury is better known as the birthplace of Charles Ives (1874-1954), arguably the greatest American musical composer.

Danburite was discovered by Charles Upham Shephard (1804-1866), an eminent American mineralogist who was for many years professor of natural history at Amherst College. Shepard began his career as assistant to Benjamin Silliman at Yale University.

Danburite is usually colorless to very light pink in color, but some deposits may produce specimens in shades of light yellow or brown. Danburite is known for its excellent transparency and clarity.

By chemical composition, danburite is a calcium aluminum borate silicate. It is quite hard, with a rating of 7 to 7.5 on the Mohs scale. Since it has a reasonably high refractive index (6.30 to 6.36), in the same range as tourmaline, the material can be faceted with good results. Danburite has very little cleavage, so it is easy for lapidaries to cut. Danburite's density is 2.97 to 3.03, about the same as jadeite.

Danburite Crystal

Though danburite was first discovered in Danbury, Connecticut, the original deposit is buried under the city. Other deposits have been found in Burma, Japan, Madagascar, Mexico and Russia. Much of the danburite in today's market comes from Mexico.

Market interest in danburite derives from the fact that there are relatively few hard clear gems available at an affordable price. Since danburite can be found in larger sizes -- often up to 10 carats -- it completes mainly with rock crystal (quartz), white topaz and white zircon.

First Published: January-18-2010

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