A Guide to Colored Gemstones in Fine Jewellery
Diamonds get graded on the 4Cs, but colored gemstones follow a different logic entirely — hardness, treatment, and species matter more than a universal grading scale. Understanding these makes it much easier to judge what you're actually buying, and how to look after it afterward.
Hardness: the Mohs scale
Mohs hardness measures relative scratch resistance, from 1 (talc) to 10 (diamond). It's a genuinely practical thing to know before buying, since it determines how carefully a stone needs to be set and worn:
- Quartz family (amethyst, citrine) — around 7
- Emerald — around 7.5–8
- Sapphire and ruby (both corundum) — 9
Lower-hardness stones — opal, pearl, emerald — need more careful setting and more deliberate daily-wear habits than harder stones like sapphire.
Common stones, and what actually makes them different
Ruby and sapphire
Both are corundum — color is the only real difference. Red corundum is called ruby; every other color is called sapphire. Heat treatment to improve color or clarity is common in this category and should always be disclosed.
Emerald
Part of the beryl family, almost always showing some visible inclusion (sometimes called "jardin"), and frequently oil-treated to improve clarity — again, something that should be disclosed rather than assumed away.
Opal
Soft and genuinely water-sensitive. It can crack with extreme dryness or sudden temperature swings, so it needs specific care — not the generic "clean with a soft cloth" advice that works for harder stones.
Pearl
Organic, not mineral. Soft, and sensitive to chemicals — perfume, hairspray, and acidic skin contact all degrade it over time. Strung pearls need periodic restringing.
Amethyst, citrine, topaz, garnet, peridot
Common, harder, and generally lower-maintenance than the stones above — but still worth confirming whether a specific stone has been heat-treated or irradiated before assuming it's natural and untreated.
Treatment disclosure isn't optional
Heat treatment, oiling or resin filling, dyeing, and irradiation are all standard industry practices — none of them are a problem to disclose, but all of them need to be disclosed, per stone and per product. The same goes for synthetic (lab-created) colored gemstones: they should be as clearly labeled as lab-grown diamonds.
Caring for colored gemstones
A few habits protect most stones: avoid ultrasonic cleaners on anything that can't tolerate them (emerald, opal, most treated stones), keep stones away from direct perfume or chemical contact, and store pieces separately so harder stones don't scratch softer ones.
Every gemstone specification on a Divara listing — species, treatment, origin, and weight — reflects that specific piece's actual documentation. Explore our gemstone jewellery to see current pieces.