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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

Alexandrite

Alexandrite is a variety of chrysoberyl that can look green in daylight and red to purplish red by lamp or candle. Learn what causes the change, how quality is judged and how to spot imitations.

Classification
Mineral variety
Mohs hardness
8.5 (scratch resistance — one part of durability)
Wear considerations
Alexandrite is 8.5 on the Mohs scale, with excellent toughness and no cleavage, which makes it a good choice for rings and everyday wear. A fracture-filled stone should only be cleaned with warm, soapy water. [cite ref="s5"]
Treatment
Laboratory-grown material is common — disclose
Care
Warm, soapy water is always a safe way to clean alexandrite. Ultrasonic and steam cleaners are usually safe as well. Alexandrites are usually not treated, but some have fractures. A fracture-filled stone…
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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.