Stone Guide
A Field Guide to Colored Gemstones
Colored gemstones cluster into a few mineral families, and the family tells you more than the marketing name. Corundum (ruby, sapphire) and beryl (emerald, aquamarine) are the hardest and best known; quartz (amethyst, citrine) sits right at the daily-wear cutoff of 7; opal, turquoise and pearl are softer and porous, and need gentler handling than anything else in this guide.
"Colored gemstone" sounds like one category, but almost every familiar name belongs to one of a handful of actual minerals, and that mineral — not the trade name — determines how the stone wears. Two stones with completely different names can be chemically the same thing in a different color, and two stones that look similar can come from unrelated minerals with very different durability.
Corundum: ruby and sapphire
Ruby and sapphire are both corundum — aluminum oxide — and the only real difference between them is a trace element. Chromium turns corundum red and the stone is called ruby; almost any other trace element or color, including the blue caused by iron and titanium together, is called sapphire. At 9 on the Mohs scale, corundum is the hardest natural gemstone after diamond, which is why both have been the default choice for engagement and heirloom pieces for centuries.
Beryl: emerald, aquamarine, morganite
The same pattern repeats with beryl. Chromium and vanadium produce the green of emerald; iron produces the blue-green of aquamarine; manganese produces the pink of morganite. Beryl sits at 7.5 to 8 on the Mohs scale, which looks durable on paper — but emerald is the exception in its own family. Emeralds grow with internal fractures (the trade calls this garden, or jardin, in French) that make them noticeably more brittle than the hardness number implies, which is why almost every emerald on the market has been oiled or resin-filled to reduce the visibility of those inclusions. Aquamarine and morganite don't share this problem and wear closer to what their hardness suggests.
Quartz: amethyst, citrine, smoky quartz
Amethyst and citrine are both quartz, colored by iron impurities and the radiation the crystal was exposed to underground — and the two are more closely related in practice than most buyers realize, since most citrine on the market today is heat-treated amethyst, not a separately mined yellow stone. Quartz sits at 7 on the Mohs scale, which is the threshold this site's other stone guides keep coming back to: 7 is the hardness of the dust in ordinary air, so anything at or above it holds its polish through daily handling, and anything below gradually doesn't.
| Stone | Mineral family | Mohs hardness | Color comes from |
|---|---|---|---|
| Ruby / sapphire | Corundum | 9 | Trace chromium (ruby) or iron/titanium (blue sapphire) |
| Spinel | Spinel | 8 | Trace chromium or iron, depending on color |
| Topaz | Topaz | 8 | Trace impurities; often irradiated/heat-treated for blue |
| Emerald / aquamarine / morganite | Beryl | 7.5 - 8 | Trace chromium/vanadium, iron, or manganese |
| Amethyst / citrine / smoky quartz | Quartz | 7 | Iron impurities plus natural or induced irradiation |
| Tourmaline | Tourmaline | 7 - 7.5 | Varies — one of the most chemically varied gem groups |
| Garnet | Garnet | 6.5 - 7.5 | Iron, manganese or chromium, depending on the species |
| Peridot | Olivine | 6.5 - 7 | Iron — intrinsic to the mineral, not a trace impurity |
| Tanzanite | Zoisite | 6 - 7 | Trace vanadium, heat-treated to intensify the blue-violet |
| Opal | Hydrated silica | 5.5 - 6.5 | Light diffraction off internal silica spheres, not pigment |
| Turquoise | Turquoise | 5 - 6 | Copper (blue) and iron (green) |
| Pearl | Organic (calcium carbonate) | 2.5 - 4.5 | Layered nacre, not a mineral color at all |
The soft cluster: opal, turquoise, pearl
Three stones on that list are meaningfully softer than the rest, and each is fragile for a different reason. Opal contains 5 to 20 percent water within its structure — it can craze or crack if it dries out or meets sudden temperature change, which is why opal jewelry shouldn't go from a warm pocket into cold water. Turquoise is porous, so it absorbs skin oil, lotion and perfume over time and can shift color as a result. Pearl isn't a mineral at all — it's layered calcium carbonate secreted by a mollusk — and at 2.5 to 4.5 on the Mohs scale it scratches easily and is attacked by anything acidic, including the citric acid in perfume and the acetic acid in vinegar. All three share one rule: put them on last, after makeup and perfume, and take them off first.
Where this leaves what we actually stock
This guide is deliberately broader than Revoulou's own lineup — it's a reference for the colored-stone world generally, not a list of what's for sale here. Our own comparison of moissanite, cubic zirconia and lab-grown diamond covers the colorless side of that world in the same depth. Pearl is the one stone above that we do carry, and it's worth knowing it needs the gentler handling described here — softer and more reactive than the moissanite, cubic zirconia and lab-grown diamond our existing care guide was written for.
If you're trying to place a birthday against this list rather than just browsing it, see our birthstone-by-month guide for the calendar version, or our sun-sign guide for the element-based system our Birth Chart tool actually uses.
