Tanzanite
Zoisite var. Tanzanite · Precious Gemstone
Crystal System
Orthorhombic; typically forms prismatic crystals with striated faces
Mineral Group
Silicates - Sorosilicates
Chemical Formula
Ca2Al3(SiO4)(Si2O7)O(OH) with trace Vanadium
Formation Process
Metamorphic, specifically formed during complex tectonic and metamorphic events involving Pan-African orogeny under high-pressure and medium-to-high temperature conditions
About This Crystal
Spherical polished bead displaying a vibrant blue-violet to deep indigo color with vitreous luster, showcasing typical trichroism and depth of color found in heat-treated tanzanite gemstones
Physical Characteristics
Blue to violet body color, white streak, distinct cleavage in one direction, conchoidal to uneven fracture, specific gravity around 3.35, brittle tenacity, no significant magnetism or fluorescence
Optical Properties
Biaxial positive optical character, strong trichroism displaying blue, violet, and brownish-yellow/red depending on viewing angle, refractive index of 1.691-1.700, high birefringence of 0.009 to 0.01
Hardness & Durability
Origin Region
Merelani Hills, Lelatema Mountains, Manyara Region, Tanzania; formed in metamorphic environments
Hardness & Durability
Mohs hardness of 6 to 7, fair toughness, sensitive to rapid temperature changes (thermal shock) and strong acids, requires careful handling in jewelry
Care & Maintenance
Clean with warm soapy water using a soft brush, avoid ultrasonic and steam cleaners, store separately to prevent scratching from harder stones like quartz or corundum
Rarity & Value
Rare; found exclusively in one location worldwide in northern Tanzania, value determined primarily by intense color saturation, clarity, and cut, commonly heat-treated to enhance blue color
Special Characteristics
Pronounced trichroism, intense pleochroic shifts observable from different crystal axes, high saturation of violet-blue color after standard heat treatment
Lore & History
Discovered in 1967 and named by Tiffany & Co. after its country of origin, modern birthstone for December, traditionally associated with the third eye and throat chakras to promote spiritual awareness and communication