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

Black onyx

Cabochon: mottled

True onyx is chalcedony banded black and white; the solid black onyx sold in jewelry is almost always gray chalcedony dyed black, since evenly black stones are very rare in nature. Its waxy polish and even color make it a staple for beads, cabochons and cameos.

Price

$0.80 to $11 per carat

Cabochons $0.80 to $5/ct; faceted onyx $1 to $7/ct at the lower end and $6 to $11/ct at the higher end.

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: An even, deep black and a good polish, then the work: faceted cuts and carvings cost more than cabochons and beads because they take more time and skill. Most black onyx is dyed, so stones sold as untreated are worth asking about.
Wear and care: Plain water and a soft brush; skip soap, which porous treated stones can absorb and dull. Avoid ammonia and other household chemicals, ultrasonic cleaners and contact with harder gems.
Look-alikes: Black obsidian looks almost identical, but onyx is heavier and can show banding. Black glass, augite and black spinel are also passed off as onyx.

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