The lapidary guides: learning to read stones

Identifying a stone is good. Understanding what you hold in your hand is better. The lapidary guides gather the craft knowledge that gemmologists, mineralogists and jewellers take years to accumulate, explained simply and illustrated so you can use it today, loupe in hand.

Telling the real from the fake

The guide to inclusions is probably the most valuable of the set: with a 10x gemmological loupe costing very little, you will learn to read the inside of a gem like an open book. The “garden” of a natural emerald, the rutile needles in quartz, the silk of sapphire, the three-phase inclusions of Colombian emeralds: all signatures of authenticity. Conversely, perfectly round bubbles betray glass, and curved growth striae expose a laboratory ruby or sapphire. This guide makes you a stone detective — and complements the authenticity-check mode of our AI identification perfectly.

The guide to gem treatments continues the investigation. Almost all commercial sapphires and rubies are heated, emeralds have been oiled for centuries, blue topaz is nearly always irradiated: these treatments are accepted by the market, stable and perfectly legal — provided they are declared, as French law requires. Others should alert you: beryllium surface diffusion, rubies rebuilt with lead glass, dyed howlite sold as turquoise, quartz coated with an iridescent film. Knowing the difference means not paying a natural stone's price for a treated one.

The porcelain streak test is the founding gesture of the mineralogist: rub the mineral on the unglazed underside of a mug and look at the colour of the powder. It is far more reliable than the stone's apparent colour: hematite, whether grey, black or reddish, always leaves a red-brown streak; golden pyrite — “fool's gold” — leaves a greenish-black streak, while real gold leaves a yellow one. Generations of prospectors were saved from ruin by this zero-cost test.

Understanding gems and metals

The guide to gem cuts decodes the eight classic cuts — round brilliant, princess, emerald, cushion, oval, pear, marquise, cabochon — and explains why each exists: the emerald step cut was invented to spare a fragile stone and reveal its clarity, the 57-facet brilliant to maximise a diamond's fire, the cabochon to release the star of asteriated sapphires. The anatomy of a cut gem completes the picture by naming each part — table, crown, girdle, pavilion, culet — and explaining their optical role: a pavilion that is too deep or too shallow and light “leaks”, leaving the stone lifeless despite its quality.

On pure mineralogy, the guide to the seven crystal systems reveals the internal geometry of minerals — cubic for diamond and fluorite, trigonal for quartz and ruby, monoclinic for jade — while the guide to geological formation tells the three great ways a stone comes into the world: igneous in cooled pockets of lava, metamorphic under the pressure of tectonic plates, sedimentary drop by drop in the fissures of rock.

For jewellery, the guide to precious metals teaches you to read an alloy — 18-karat gold (750‰), 14-karat, 9-karat, sterling silver 925, platinum 950, and the essential difference between vermeil and simple plating — while the guide to French hallmarks puts before your eyes the marks every bargain-hunter should know: the eagle's head of 750 gold, the Minerva of solid silver, the dog's head of platinum, the lozenge of the maker's mark. These tiny impressions, hidden inside a ring band or on a clasp, are worth all the certificates in the world.

Displaying and photographing

The guide “Photographing stones well” gives you the five habits that change everything: indirect daylight, never flash, a neutral matte background, a cleaned stone, several angles, tight framing. These tips improve your listings and your collection photographs — and markedly increase the accuracy of Lapidem's AI identification. Finally, the guide to display lighting reveals the colour temperatures that flatter each stone (cool LED for a diamond's fire, warm white for amber and citrine), the importance of a colour rendering index above 90, and the dealers' secret: “north light”, that indirect daylight which remains the absolute benchmark for judging a gem's colour honestly.

And because a stone is also a story, the timeline “Stones through history” takes you from the first Afghan lapis lazuli mines, opened 6,500 years ago, to today's laboratory diamonds, by way of Tutankhamun's mask, Cleopatra's emeralds, the first diamond engagement ring of 1477 and the discovery of the Cullinan, the largest rough diamond ever found.