Zoisite

Characteristics

• Habit - prismatic
• Form - orthorhombic
• Hardness - 6-7
• Cleavage - perfect
• Fracture - concoidal to uneven
• Streak - white
• Lustre - vitreous
• Colour - grey, white, light brown, yellowish-green, pale greenish-grey, pink, lilac to blue

Calcium aluminium silicate hydroxide. Results from metamorphism of calcium rich rocks occurring in schists, gneisses and amphibolites. Also found in veins of quartz and pegmatites. Crystals exhibit grey, purple or blue colours depending on the angle of view.

Tanzanite

Blue to violet so often mistaken for sapphire. Strong trichroism of blue, yellow and pale pink to purple. Can be heat treated to improve colour and then shows only two colours of blue & purple.

can occur as green and yellow and be called 'yellow tanzanite' but the 'tanzanite' refers to the vlue variety so the other should be called 'yellow zoisite'.

First discovered in 1967 at the Merelani mine in Tanzania. Not found elsewhere. Soft for a gem, not very tough so wear with care. Perfect cleavage makes it better for necklaces, earrings or dress wear.

It's important to cut it to show the best colours of deep blue with shade of purple being most desirable.