silicates
Emerald
Be3Al2Si6O18
- Crystal system
- hexagonal
- Hardness
- 7.5–8 on the Mohs scale
- Lustre
- vitreous
- Colour
- Green, from grass to deep forest
- Where it forms
- Unusually, since it needs beryllium and chromium in the same place, and those elements normally occur in entirely different rocks. The Colombian deposits formed where brines moved through black shales, which is geologically distinctive.
- Chiefly from
- Boyaca, ColombiaZambiaBrazilEthiopia
Why it is that colour
Chromium, and sometimes vanadium, substituting for aluminium. The trade requires the green to be saturated enough; paler chromium-bearing beryl is sold as green beryl instead, and where the line falls is a commercial judgement rather than a mineralogical one.
Safety
Safe to handle. As with all beryl, cutting produces beryllium-bearing dust that should not be inhaled. Emeralds are also routinely oil-filled to hide fractures, and that treatment is disturbed by ultrasonic cleaning.
Where it comes from
Colombia has produced the finest material for five hundred years, and Colombian emerald mining has a long and violent history including the guaqueria wars of the 1980s. Zambian production is largely industrial and more traceable. Nearly all emerald on the market is fracture-filled with oil or resin, and disclosure standards vary.
Historical use
Taken from Egypt to Rome, and from Colombia to Europe and Mughal India in enormous quantity after the Spanish conquest. Many of the great Mughal emeralds are Colombian stones carried east through Spanish and Portuguese trade.
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
Egyptian mines in the eastern desert, later called Cleopatra’s mines, were worked from around 1500 BC. Emerald appears throughout classical, biblical and Vedic sources, and Pliny writes that green rests the eyes — advice repeated for centuries. Modern associations with the heart and with truth are later.
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
Emeralds are almost always full of inclusions, and unusually the trade has made peace with this rather than treating it as a defect. The French term is jardin, garden, for the tangle of fractures and crystals inside a stone. A flawless emerald is more likely to be synthetic than exceptional.
Those inclusions turn out to be forensically useful. Because the mineral assemblage trapped inside a stone reflects the rock it grew in, gemmologists can often say which deposit an emerald came from — which has been used to trace historic stones and to show that emeralds in Mughal and Ottoman treasuries were mined in Colombia after 1500.
Identity checked against IMA-CNMNC master list, June 2025.