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Discovery
Tanzanite was discovered in 1967 near Arusha, Tanzania in Africa. It belongs to the epidate mineral group that are derived from 500 million-year-old metamorphic rocks.
Other Names
Natural tanzanite is also called tanzanite blue, PDF 13-562, Anyolite-green, Thulite-red and ICSD 66924.
Physical Properties
Natural tanzanite rates 6.5 on the Mohs scale of mineral hardness (the scale rates the scratch-resistant properties of various gemstones and minerals, with 1 being the softest and 10 being the hardest). Tanzanite is softer than other gemstones, such as tourmaline and topaz. It occurs in various habits, including columnar, striated and prismatic.
Tanzanite has a specific gravity between 3.2 and 3.4 (the specific gravity of a substance is its density in comparison with the density of water) and has an orthorhombic crystal system. It is 48.67 percent oxygen, 19.71 percent silicon, 18.76 percent calcium, 12.63 percent aluminum and 0.24 percent hydrogen. The molecular weight (the sum of the individual atomic weights of its atomic components) of tanzanite is 427.38 gm and its refractive index (the ratio of the velocity of light in air and the velocity of light in a particular substance) lies between 1.69 and 1.70.
Metaphysical Properties
The American Gem Trade Association lists tanzanite as a December birthstone. According to "The Encyclopedia of Crystals," tanzanite is beneficial for anxiety, depression, reducing inflammation, cell regeneration, spleen and the immune system. "The Encyclopedia of Crystals" claims that the stone influences deep meditation and evens out energy fluctuations.
Color
Natural, mined tanzanite is typically reddish/orange brown. It turns into a violet blue when heated to 300 to 600 degrees Celsius (depending on the size of the crystal). Heating rearranges the atoms of tanzanite and dissociates the yellow component from its crystal matrix, leaving behind blue and purple. The heat treatment is permanent, and tanzanite retains its blue color.
Types/Cuts
Natural tanzanite is cut to different shapes. Popular shapes include cushion (square shaped), marquise (drop shaped), oval, tanzanite emcut (cut to a bezel shape), round, heart, trilliant and pear.
Jewelry
Tanzanite is a popular ring stone, but it is susceptible to scratches and abrasions under rough use. It is set in tie pins, pendants, bracelets and earrings.