• 
• 
• 
• 

Tanzanite

Zoisite occurs in a number of varieties, the most sought-after being Tanzanite, a variety coloured sapphire-blue by the presence of vanadium. Tanzanite crystals have distinct pleochroism, showing purple, blue, or slate-grey depending on the angle they are viewed from. Their may also be a slight colour change in incandesce (such as that from a light bulb), when stones may appear more violet. A massive green variety of zoisite, containing rubies and occasionally dark horn-blende inclusions, may be polished, carved, or tumbled to make ornaments or an attractive decorative stone. Thulite, a massive, pinkish red variety coloured by manganese, is also polished or carved to make small ornaments. Tanzanite has been confused with sapphire, and thulite with rhodonite. Some heating of zoisite varieties may enhance their colour.

Occurrence

Tanzanite was first found in Tanzania (hence the name). Yellow and green zoisite occurs in Tanzania and Kenya. Thulite is found in Norway, Austria, western Australia, Italy, and North Carolina (USA).

Remark

Discovered by Baron von Zois in the Sau-Alp mountains of Austria, zoisite was first called saualpite.

Crystal structure	Orthorhombic
Composition	Calcium aluminium hydroxysilicate
Hardness	6.5
SG	3.35
Rl	1.69-1.70
DR	0.010
Lustre	Vitreous