Emerald
Beryl coloured green by chromium — and the one major gemstone whose inclusions are expected rather than a fault.
Emerald is beryl coloured green by chromium, vanadium, or both. Beryl is otherwise colourless; every named beryl variety is the same mineral with a different trace element in it, and emerald is the one that made the mineral famous.
What sets emerald apart from every other major gemstone is that it is expected to be included. Its formation environment brings beryllium — rare and usually confined to granitic settings — into contact with chromium, which occurs in quite different rocks, and the geology that manages it is violent enough that the crystals grow flawed. The trade calls the internal landscape the jardin, garden, and a clean emerald is not a better example of the species so much as a suspicious one.
Those inclusions make it brittle for its hardness. It scratches like quartz and above, and it chips and cleaves in a way that means an emerald ring is not an everyday ring.
How to identify it
Green, hexagonal prisms, and a refractive index and density lower than most green stones it might be confused with — tsavorite garnet and green tourmaline are both denser. Under filtered light chromium-coloured emerald typically shows red, which vanadium-coloured stones do not.
The inclusions are diagnostic in themselves: a stone sold as emerald with no inclusions at all is more likely to be synthetic or green glass than an exceptional natural one.
Uses
Almost entirely gemstone use, and it is among the most valuable of them — a fine Colombian emerald can exceed diamond per carat.
Oiling is near-universal and is disclosed rather than hidden: cedar oil or a polymer of similar refractive index is drawn into the surface-reaching fractures, which makes them far less visible. It is not permanent, it can be redone, and heat or ultrasonic cleaning removes it — which is why an emerald must not go in an ultrasonic cleaner.
Name origin
Through Old French and Latin from the Greek smaragdos, a word applied loosely in antiquity to a range of green stones, and ultimately from a Semitic root. The Egyptian mines of the Red Sea hills, worked from the Ptolemaic period and known as Cleopatra's mines, are the oldest documented source.
How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.
How this connects
Where a connection has been confirmed by an outside reference, that reference is named beside it.
is a variety of
- Beryl — mineral · coloured green by chromium, vanadium or both — the same mineral as aquamarine and morganite
contains
is used in
- Mining and quarrying — industry · and its deposits are worked by a mixture of large operations and informal mining, particularly in Colombia
is commonly confused with
- Aquamarine — mineral variety · one mineral and two trace elements — the same hardness, density and crystal system, and a price difference of orders of magnitude
- Peridot — mineral variety · several famous historic 'emeralds' in European treasuries have turned out to be peridot, which is a softer, yellower green and far more strongly doubly refractive
is an alternative to
- Peridot — mineral variety · as a green stone at a fraction of the price, and it is a different green — yellower, and doubly refractive enough to see
is used as
- Jewellery and adornment — application · and almost always fractured and oiled, because beryl grows with inclusions and the trade has treated them for centuries
Sources
- Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
- Material WorldOur own writing