Color-Change Diaspore

In the centuries that man has been scouring the earth for valuable minerals, one would think that all the different types of gemstones had already been discovered. But new ones seem to be found on a fairly regular basis, and some of these have become very important in the market.

Tanzanite was discovered only in the 1960's, and tsavorite garnet in the 1970's, both in East Africa. Chrome diopside was first found in Russia in the 1980's, and paraiba tourmaline from Brazil first came on the market in the early 1990's. More recently there has been a lot of publicity surrounding andesine labradorite, though no one is still quite sure where it comes from and whether it has been treated.

Color-Change Alexandrite

The latest new find in the gems world is a delicately-colored stone with interesting color-change properties being promoted under the name zultanite. Mined from a single deposit in the mountains of central Turkey, the name zultanite is a brand name introduced by the man with mining rights to the deposit, Murat Akgun. We assume the name is supposed to reference the sultans who ruled the Ottoman Empire.

Color-Change Sapphire

The name zultanite may be new, but this particular mineral has been known since 1801 when it was first discovered in the Ural Mountains in Russia. Its gemological name is diaspore, and it is a hydrated aluminum oxide colored by manganese. It was first faceted as a gemstone in the 1980's, but has never been mined commercially until recently.

Diaspore has reasonably good gemstone characteristics. It has a hardness of 6.5 to 7 on the Mohs scale, comparable to peridot and tanzanite. It has a refractive index of 1.702-1.750, between tanzanite and spinel. Diaspore does have perfect cleavage in one direction, making it a challenge to cut.

Color-Change Garnet

Gems that change color under different lighting are rare and diapsore is attracting buyers drawn to this unique quality. Under natural or fluorescent light, diapsore has a kiwi green color, with flashes of yellow. Diaspore displays a champagne color under incandescent lighting, and when exposed to subdued lighting, such as candlelight, it has a pinkish color. The larger the stone, the more pronounced the color change effect will be.

Diaspore deposits have now been found in a number of locations around the world, including Arizona and Pennsylvania in the USA, New Zealand, Brazil, Argentina, Russia, UK and China. But thus far the only gem-quality material has been mined in Turkey.