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Gemstone encyclopedia

Every gemstone, explained

What each stone is, how it wears in jewellery, and what to ask before you choose one. Browse by colour, or go straight to a letter.

This encyclopedia is educational. Inclusion does not confirm current Ralph Jacobs stock, sourcing, availability or suitability for a particular jewellery design.

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Quick overview · December · Birthstone list as given by GIA

Tanzanite

Tanzanite is the blue-violet variety of zoisite, mined commercially only in Tanzania's Merelani Hills. Learn how its colour is judged, why most is heated, and how to protect it.

Classification
Mineral variety
Mohs hardness
6–7 (scratch resistance — one part of durability)
Wear considerations
Tanzanite is 6 to 7 on the Mohs scale, with fair to poor toughness and cleavage, so it can break when struck. It can still be worn in all types of jewellery if it is protected from rough wear and hard blows.
Treatment
Heat treatment (routine and stable; most blue tanzanite owes its colour to heating), Coating (rare and not permanent), Fracture filling (uncommon)
Care
Clean tanzanite in warm, soapy water. Ultrasonic and steam cleaners are not recommended for it. Keep it away from very high heat, sudden temperature changes, and hydrochloric and hydrofluoric acids. Protect it…
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Individual gemstones vary. Care depends on treatment, setting and condition. Encyclopedia inclusion does not confirm availability.

Individual gemstones vary · care depends on treatment, setting and condition · birthstone traditions vary · encyclopedia inclusion does not confirm availability.