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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

Amethyst

Amethyst is the purple variety of quartz. This entry explains how its colour and clarity are judged, how it wears, whether its colour can fade, and which treatments to ask about.

Classification
Mineral variety
Mohs hardness
7 (scratch resistance — one part of durability)
Wear considerations
Amethyst rates 7 on the Mohs scale and has good toughness, so it suits all jewellery types, including rings, if the wearer understands the limits of its hardness. Sand and dust are mostly quartz and can scratch it. Sudden temperature changes can cause it to fracture, and some amethyst colour can fade with prolonged exposure to intense light.
Treatment
Heat treatment to lighten very dark amethyst, Dyeing of lower-quality light amethyst or light quartz to a purple colour, Fracture filling of surface-reaching cracks to improve apparent clarity (rare)
Care
Warm soapy water is a safe way to clean amethyst. An ultrasonic cleaner is usually safe too, except for rare dyed or fracture-filled stones. Steam cleaning is not recommended. Keep amethyst away…
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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.