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.
3 of 27 gemstone entries
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Alexandrite
Hardness 8.5
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Amethyst
Hardness 7
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Aquamarine
Hardness 7.5–8 · March
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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…
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.