organic
Pearl
- Also known as
- nacremother of pearl
- Crystal system
- orthorhombic
- Hardness
- 2.5–4.5 on the Mohs scale
- Lustre
- pearly
- Colour
- White, cream, gold, grey, black, with iridescent overtones
- Where it forms
- By a mollusc, as a defence: layers of nacre deposited around an irritant. Natural pearls are extremely rare. Cultured pearls are produced by deliberately inserting a nucleus, a technique perfected by Kokichi Mikimoto by 1916.
- Chiefly from
- Persian GulfJapanFrench PolynesiaAustraliaChina
Why it is that colour
The lustre is not pigment. Nacre is built of microscopic aragonite platelets stacked in layers about as thick as a wavelength of light, and the shimmer is interference between reflections from successive layers.
Safety
Safe to handle. Aragonite is soft and dissolves in acid, so pearls are damaged by perfume, hairspray, vinegar and sweat. The old rule about putting pearls on last is chemistry.
Where it comes from
Natural pearl fishing in the Persian Gulf sustained whole economies until the 1930s, when Japanese cultured pearls collapsed the market within a decade. Almost all pearls sold today are cultured, most freshwater ones in China, and this is disclosed as standard. Freshwater pearl mussels are endangered in much of Europe, and unlicensed fishing for them in Scottish rivers is a criminal offence.
Historical use
Cleopatra is said by Pliny to have dissolved a pearl in vinegar and drunk it to win a wager about the most expensive meal — chemically plausible, since aragonite does dissolve in acetic acid, though it takes rather longer than the story allows.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
What is attributed to it, and since when
Ancient and near-universal, appearing in Roman, Persian, Indian, Chinese and biblical sources, consistently as a symbol of purity and of great value. The parable of the pearl of great price assumes an audience that knows what one costs.
Described, not endorsed. Dating a claim is not the same as assessing it — but an association that first appears in a book published in 1985 is not an ancient inheritance, whatever the label says. A sincere account of feeling better is compatible with the stone doing nothing — see the placebo effect.
Sold as this, but not
Worth knowing
Pearls are the only gem produced by a living animal as a response to injury, and the only one that requires no cutting — it emerges finished.
The cultured pearl is one of the more interesting economic events in the history of gems. Mikimoto and his contemporaries worked out how to induce the process reliably in the early twentieth century, and within twenty years natural pearls had ceased to be a significant market. Whole Gulf economies that had depended on pearl diving for centuries were ruined, shortly before oil arrived. A cultured pearl is a real pearl in every material sense — same animal, same nacre, same process — and that is exactly why the natural trade could not survive it.
Identity checked against IMA-CNMNC master list, June 2025.