Tanzanite

Tanzanite is the blue to purple transparent variety of the mineral zoisite.  It was first discovered in the 1960’s at the foothills of Mt Kilimanjaro in Tanzania where it is the only known source.  Due to this the name tanzanite was coined by Tiffany and Co. Jewellers in honour of its sole country of origin.  Tanzanite is now one of the most desirable gemstone on the market today despite its short history.  You only have to look in to its deep alluring colour to see why.  Virtually all tanzanite is heat treated as this is how the blue to purple colour is derived from that original material.  Some rare specimens of tanzanite naturally occur blue without the aid of man.  These stones are assumed to have undergone some form of natural heating and can produce exceptionally rare blue and green ‘bi-colour’ tanzanite.  Tanzanite is available in a myriad of sizes, although smaller sizes of fewer than 2ct seem to lose their intense deep colour and appear washed out.  The most intense and entrancing colours of tanzanite are seen in the larger stones and can be obtained in fine qualities of well over 10 carats.
Video of much of our tanzanite stock can be viewed at our website.


Mohs’ Hardness: 6.5-7
Specific Gravity: 3.15-3.58
Refractive Index: 1.692-1.700
Birefringence: 0.006-0.013
Optic Sign & Character: Biaxial Positive
ICA Code: H
Treatments: Heating
Incidence: Extremely common
Purpose: To induce blue colour and reduce trichroism
Durability: Poor to reasonable
Special Care: Avoid knocks, ultrasonics and acids
Synthetics: None
Possible Imitations: Synthetic sapphire, Synthetic spinel, CZ, synthetic forsterite