Know a gemstone before you buy one.

104 stones, rendered live from their real optics. Turn one, see it cut or as it comes out of the ground, hold it under a UV lamp. Then read what it costs per carat, how to wear it, how to tell it from a fake and what it has meant to people.

Explore the stones Or start with a ruby from Mogok

A ruby from Mogok, Myanmar, traced from its optics: a render, not a photograph.

The collection

Shelved by where each stone is mined.

Golden pagodas on terraced hills above a valley in morning mist

Burma and Southeast Asia6

The Mogok valley in Myanmar has given rubies and red spinels grown in marble for centuries, and Burma on a lab report still sets the price of a ruby. Blue zircon comes from the basalt country of Cambodia.

Tea terraces and a red earth path above a river with pale gravel diggings

Ceylon and East Africa22

One belt of rock, folded when Gondwana came together about 600 million years ago, runs from Mozambique to Ethiopia and on through Madagascar and Sri Lanka. It feeds the gem gravels of Ceylon and the mines of Tanzania and Kenya, which is why a sapphire from Madagascar can look just like one from Sri Lanka.

A green Andean valley under low cloud, a river at its floor

Colombia and Brazil24

Colombian emerald grows in veins through black shale and is the benchmark for the stone. The pegmatites and veins of Minas Gerais and Bahia give beryl, topaz, tourmaline and quartz, and the old lava flows of the south hold amethyst geodes.

Red earth, acacias and flat-topped hills of the Karoo at sunset

Southern Africa8

Diamonds ride up from the mantle in kimberlite pipes; the first were found in South Africa in the 1860s. Tiger's eye is quartz that took the place of blue asbestos fibers in the banded iron rocks of the Northern Cape. The Cullinan mine gives most of the rare blue diamonds.

Birch and pine forest along a mountain stream in autumn

The Urals and Europe13

The Urals gave the Russian court its own gems: alexandrite, found in 1833, and demantoid in 1851. Europe keeps some of the classic localities of collector minerals, like the pyrite cubes of Navajún, English fluorite and the hyalite of Valec, which glows green under UV.

Pale opal diggings on red outback earth under a blue dusk sky

Australia7

Black opal, the most valued kind, comes from Lightning Ridge in New South Wales, formed in the sediments of an old inland sea. In Queensland, opal filled the cracks of ironstone boulders, and in the Kimberley the Argyle mine gave almost every pink diamond in the world until it closed in 2020.

Dark lava rocks and sagebrush below a snow-capped volcano at sunset

North America21

Stones from volcanic rock and old shields: peridot carried up in basalt at San Carlos, copper sunstone in Oregon lava, fire agate in Mexico, labradorite from the Canadian Shield. Kunzite comes from the pegmatites of southern California, and hackmanite, which changes color with light, from Mont Saint-Hilaire in Quebec. Two classics of fluorescence are here too: benitoite, from a single mine in California, and the willemite ore of Franklin, New Jersey.

A dim laboratory with glassware lit inside a growth chamber

Made in a lab3

Stones made, not mined. Flame fusion ruby, from 1902, was the first; lab grown diamond is the same carbon crystal grown in weeks; and moissanite exists in nature only as microscopic grains, so every gem of it is grown. None has a provenance, and a lab report says so.

Chalcedony (quartz) · Brazil

Red onyx

Cabochon: mottled

Chalcedony, a microcrystalline quartz, dyed an even red; translucent at thin edges, otherwise near opaque. Despite the name it is usually unbanded: true onyx has parallel bands, and the naturally red banded kind is sardonyx.

Price

$0.80 to $5 per carat

Onyx cabochons in general; no guide prices red onyx on its own.

Source: Gem Rock Auctions, Feb 2026. Asking prices, not an appraisal.

Hardness6.5 to 7

Mohs scale, 1 to 10. Household dust contains quartz (7), so softer stones scuff with daily wear.

What sets the price: Size and cut more than rarity: nearly all onyx on the market is treated, so treatment barely moves the price. Faceted stones and carvings cost more than cabochons because of the work involved.
Wear and care: Warm water and a soft brush, then dry with a soft cloth. Skip soap, which treated, more porous stones can absorb and dull, and keep it away from harsh chemicals such as ammonia, ultrasonic cleaners and harder gems.
Look-alikes: Carnelian, the naturally red chalcedony, and sardonyx, whose red to brown bands alternate with white or black. Crystal Vaults notes that a lot of dyed unbanded chalcedony is sold as red onyx.

Love gems? Tell us what to add or fix