Skip to content

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.

Explore birthstones
More filters

27 of 27 gemstone entries

Quick overview

Tourmaline

Tourmaline is a family of minerals with one of the widest colour ranges of any gem. Learn why, how each colour is judged, how it is treated and how well it wears.

Classification
Mineral group
Mohs hardness
7–7.5 (scratch resistance — one part of durability)
Wear considerations
Tourmaline ranks 7 to 7.5 on the Mohs scale and its toughness is rated Fair. High heat can change its colour, sudden temperature changes can cause fractures, and colour from irradiation can fade with heat or bright light.
Treatment
Heating at low temperature, used on many blue and green stones to improve or lighten their colour; often undetectable. Named here as this guide's editorial practice, not as a statement of any country's law., Irradiation, which can be used to deepen pink colour; the colour can fade with heat or bright light. Named here as this guide's editorial practice, not as a statement of any country's law., Fracture filling with oils or resins to hide cracks; generally the only one of these treatments that leaves visible evidence. Named here as this guide's editorial practice, not as a statement of any country's law.
Care
Clean tourmaline in warm, soapy water. Ultrasonic and steam cleaners are not recommended for it. Keep tourmaline away from high heat and sudden changes in temperature, which can change its colour or…
Explore the full gemstone guide

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.