The Stone Library
We have been cutting and setting stones in Jaipur for over twenty years. This is what we would tell you if you were standing at the bench: what each stone actually is, what has been done to it, how hard it is, and what will damage it.
Most of the jewellery trade doesn't volunteer this. Nearly every turquoise is stabilised, most citrine was amethyst, almost all blue topaz was colourless, and black onyx has been dyed since the Romans. None of that makes a stone fake. Not saying it is the part we object to.
The stones
- Turquoise — why it's always stabilised, what happened when Sleeping Beauty closed, and what purple Mohave really is
- Garnet — a mineral family, not a colour, and one of the very few stones never treated
- Amethyst — once as costly as ruby; how to read colour zoning, and why it can fade in sun
- Onyx — dyed chalcedony, and has been for two thousand years
- Moonstone — where the glow comes from, and what rainbow moonstone actually is
- Moss Agate — not moss, not really agate, and never the same twice
- Citrine — most of it was amethyst until it met a kiln
- Labradorite — grey from one angle, electric from another, and brutal to cut
- Malachite — beautiful, banded, and genuinely soft
- Opal — how it makes colour, and why Ethiopian opal must never be soaked
- Blue Topaz — almost all of it was colourless; hard, but with a cleavage plane
- Larimar — found in one small area of the Dominican Republic and nowhere else
- Howlite — the stone most often dyed and sold as turquoise. We sell it as howlite
Hardness at a glance
Mohs hardness measures scratch resistance, not toughness — a stone can be hard and still split. Everyday dust contains quartz at 7, which is why anything below that needs a little thought.
| Stone | Mohs | Everyday ring? |
|---|---|---|
| Blue topaz | 8 | Yes — but has a cleavage plane |
| Amethyst, citrine | 7 | Yes |
| Garnet | 6.5–7.5 | Yes |
| Onyx, moss agate | 6.5–7 | Yes |
| Moonstone, labradorite | 6–6.5 | With a protective setting |
| Turquoise | 5–6 | With care |
| Opal | 5.5–6.5 | Better as a pendant |
| Larimar | 4.5–5 | With care |
| Malachite | 3.5–4 | Bezel-set only |
| Howlite | 3.5 | Bezel-set only |
Three rules that cover most of it
- Jewellery goes on last. After perfume, hairspray, sunscreen and moisturiser — not before. Porous stones absorb all four.
- Skip the ultrasonic cleaner. It is fine for hard, clean, unfractured stones and quietly destructive to everything else on this page. Warm water, mild soap, soft brush, dry properly.
- Store stones apart. A harder stone will scratch a softer one in a shared box, every time. Individual pouches cost nothing.
Questions about a particular stone, or want to know exactly what was done to the one in a piece you're looking at? Ask us. We'll tell you.