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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

Iolite

Iolite, the gem form of cordierite, shows a blue-violet colour that shifts as you turn it. It is 7–7.5 on the Mohs scale but has cleavage, so settings and care matter.

Classification
Mineral species
Mohs hardness
7–7.5 (scratch resistance — one part of durability)
Wear considerations
Iolite is 7–7.5 on the Mohs scale, but cleavage in one direction gives it only fair toughness, which makes it vulnerable in rings exposed to rough daily wear [cite ref="s1"]. Jewellers prefer protective settings, or pieces that get less wear such as pendants and earrings [cite ref="s5"].
Treatment
Typically untreated
Care
Clean iolite with warm, soapy water and a soft toothbrush. Avoid steam cleaners and ultrasonic cleaners. Keep iolite away from high heat and sudden changes in temperature, which can cause breaks. A…
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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.