About African Gemstones
Tanzanite is a violet-blue stone first found in Tanzania in 1968 by a miner searching for sapphires. The color in this stone was caused by an ancient meteor that struck the area near Arusha, Tanzania millions of years ago, depositing the element vanadium throughout the area. Most Tanzanite is heat-treated to bring out the intense blue color. Rarely, Tanzanite is found in green, pink and yellow colors. The hardness is 6.5 to 7 on the Moh’s Hardness Scale. Due to its coloring, Tanzanite is sometimes confused with blue sapphire and amethyst.
Spinel, once thought to be a type of ruby, is chemically described as Magnesium Aluminum Oxide. It is usually found in the deep pink range but may also be yellow, orange, blue, violet, green or black. Spinel is mainly found in Burma, Cambodia, and Sri Lanka but it can be found in various other places in Asia and Africa, including Tanzania. Spinel gems were placed in the Crown Jewels of England, and were at first identified as rubies. Spinels are easy to match and make great jewelry pairings.
Zircons, often confused with man-made cubic zirconia, are natural gemstones which come in many colors. The colors for zircon are clear, blue, green, red, violet, brown and bronze. Zircons are found in Burma, Cambodia, Sri Lanka, Tanzania, and various African countries. Brown zircons are heated to create the blue varieties at 800 – 1000 degrees centigrade. Zircon has a Moh’s Hardness of 6.5 – 7.5 and is very brilliant with a high refractive index.
Garnets come in a full range of colors from green to yellow to orange to red. Their refractive index is 6.5 to 7.5. The main types are Almandine – red with violet tint, Pyrope – red, Spessartite – orange to brown-red, Grossular – green to yellow-brown. Some Tanzanian garnets display color change with different lighting. Tsavorite Garnets, found in Tanzania, are mint green to emerald green. Beautiful mint green garnets come from Merelani, Tanzania. Garnets have amazing fire, second only to diamonds.
Tourmaline, like garnet, comes in many colors. This gem also comes in multicolored forms with combinations of pink, green, orange and blue. Rubellite, the most valuable, comes in a deep red similar to ruby, but with a violet tint. The Paraiba Tourmaline is a beautiful blue-green gem that comes only from Paraiba, Brazil.
Chrysoberyl has been known for thousands of years. The most valued forms are Alexandrite and Cat’s Eye. It is a very hard gem, 8.5 on the Moh’s Hardness Scale. Alexandrite changes from green in daylight to red in artificial light.
Sphene is found in yellow, brown, green and reddish colors. It is relatively soft with a Moh’s Hardness of 5 – 5.5. It is also call Titanite due to the titanium contents.
Rubies and Sapphires make up the corundum forms. They are chemically classified as Aluminum Oxide. The light red, pink, yellow, blue and green are classified as sapphire while the reds are rubies. These stones are extremely hard – 8.8 on the Moh’s scale. Both forms are capable of forming stars, usually with six rays. Most blue sapphires are heated to clear the stone and intensify the color. There are two sapphire deposits in Montana – Phillipsburg and Eldorado Gulch, near Helena.