Guide to gem inclusions

A loupe worth a few pounds, a counterfeit detector

Inclusions are everything trapped inside a stone during its formation: crystals, liquids, gas bubbles, healed fractures. Long regarded as flaws, they have become for the gemmologist the gem's identity card: they tell where it was born, how, and above all whether it is natural. A 10x gemmological loupe, costing very little, is enough to turn you into an investigator.

The reassuring inclusions

The emerald's “garden” is the most famous: this network of veils and frosts, unique to natural emeralds, is so characteristic that a perfectly clear emerald sold cheaply should immediately arouse suspicion. The rutile needles crossing certain quartzes — “Venus hair” — are natural and highly prized by collectors. The “silk” of natural sapphires and rubies, those fine parallel needles, is a guarantee of authenticity: when well aligned it creates the star of asteriated stones.

Three-phase inclusions — a cavity containing liquid, a gas bubble and a small crystal all at once — are the hallmark of Colombian emeralds. Negative crystals, empty cavities with the perfect shape of a crystal, prove slow natural growth.

The warning signs

Perfectly round bubbles, crisp and clear: that is glass, almost certainly. No natural crystal produces spherical bubbles — they form in a molten liquid, not in crystal growth.

Curved growth striae, like the grooves of a vinyl record: that is the mark of synthetics made by the Verneuil process, which produced the first laboratory rubies as early as 1902. Natural crystals have straight striae, never curved.

Take care not to confuse synthetic and imitation: a synthetic ruby is chemically a ruby — same composition, same hardness — but its value is far lower. An imitation (glass, resin, a doublet) is not ruby at all. The law requires both to be declared at the point of sale.