Tanzanite

Found in only one place on Earth.

Mohs hardness: 6.5–7
Crystal system: Orthorhombic
Composition: Ca₂Al₃(SiO₄)₃(OH)
Colours: Violet-blue, Blue, Purple
Origins: Tanzania (Merelani Hills only)
Birthstone: December

Discovered in 1967 at the foot of Kilimanjaro, tanzanite is mined from a single 7 km stretch in northern Tanzania. Geologists estimate the deposit may be exhausted within a generation.

Strongly trichroic in the rough - showing blue, violet and burgundy from different angles - almost all gem material is heated to ~600 °C to produce the stable violet-blue.

History

A brief history

Named by Tiffany & Co. in 1968 in honour of its country of origin.

Treatments

What to know

Heat treatment - near-universal, stable, accepted

Care & handling

How to wear it

Sensitive to sudden temperature change and ultrasonic vibration
Warm soapy water only; avoid ultrasonic and steam
Best set in pendants and earrings rather than rings

Jewellery use

Setting the gemstone

Excellent for occasional-wear pieces - pendants, earrings, brooches. Suitable for rings only with protective settings and careful wear.

Famous examples

· Queen of Kilimanjaro (242 ct)
· Mawenzi (16,839 ct rough)