tanzanita

Tanzanite is a blue-to-violet gemstone variety of the mineral zoisite, a calcium aluminum silicate. It was discovered in 1967 in the Mererani Hills of northern Tanzania and soon marketed by Tiffany & Co., which coined the trade name tanzanite to emphasize its origin.

The gem is prized for strong pleochroism, displaying blue, violet, and burgundy colors when viewed from different crystallographic directions. Natural tanzanite is typically brownish or olive in tint; most stones on the market have been heat-treated to produce a vivid blue color with a violet undertone. It has a Mohs hardness of about 6.5 to 7 and can be prone to inclusions and fractures if mishandled.

Occurrence and mining: Tanzanite is found only in the Mererani Hills near Mount Kilimanjaro. The limited geographic source contributes to its relative rarity and price sensitivity within the gem market.

Care and durability: Tanzanite is susceptible to thermal shock and should be protected from rapid temperature changes, hard knocks, and ultrasonic cleaning. Clean with warm, soapy water and dry gently.

Market and authenticity: Color is largely enhanced by heat treatment; natural, untreated tanzanite is uncommon. The market also includes simulants and some lab-grown materials sold under various names. Grading and value depend on color saturation, clarity, cut, and carat weight, with the most sought-after stones showing a vivid blue-violet hue.