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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

Ruby

Ruby is the red variety of corundum, coloured by chromium. [cite ref="s1"] It is 9 on the Mohs scale and very tough, but lead-glass-filled rubies need more care. [cite ref="s3"]

Classification
Mineral variety
Mohs hardness
9 (scratch resistance — one part of durability)
Wear considerations
Untreated and heat-treated ruby is very durable: corundum is 9 on the Mohs scale, with excellent toughness and no cleavage, and fracture-filled ruby needs more care. [cite ref="s3"] Glass fillers can scratch more easily than the host stone and are more easily damaged by heat or some acids. [cite ref="s6"] In GIA testing, the lead-glass filler reacted with jewellers' pickling solution, and oven cleaner, ammonia, bleach and concentrated lemon juice etched it. [cite ref="s4"]
Treatment
Heating (for colour and/or clarity), Flux-assisted healing of fissures (fracture healing), Lead-glass filling of fractures and cavities, Diffusion, Dyeing, Coating, Synthetic overgrowth
Care
Warm soapy water is always safe for ruby. Clean rubies that are fracture-filled, cavity-filled or dyed only with a damp cloth. Ultrasonic and steam cleaners are usually safe for untreated, heat-treated and…
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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.