Peridot
Gem olivine, and one of very few gemstones that occurs in only one colour — including specimens that arrived from space.
Peridot is gem-quality olivine, magnesium-rich and coloured by iron that is part of its essential composition rather than a trace impurity. That is why it comes in one colour: the green is not an accident of contamination, so there is no colourless peridot and no blue or red one.
It is a mantle mineral. Most of it reaches the surface in basalt that carried up fragments of the mantle it melted from, which makes a cut peridot a piece of the Earth's interior rather than of its crust.
And some of it is not from Earth at all. Pallasite meteorites are iron-nickel metal with olivine crystals suspended in it, and gem-quality peridot has been cut from them — a genuinely small category of gemstone with an extraterrestrial origin.
How to identify it
A distinctive yellowish green, strong double refraction that makes the back facet edges visibly doubled through the table of a cut stone, and a density higher than the quartz and beryl varieties. The doubling is the easiest test and is visible with a loupe.
Uses
Gemstone. Its hardness of around 6.5 to 7 makes it usable but not ideal for rings, and it is sensitive to acid and to sudden temperature change.
The August birthstone, and the material of some of the largest historic gems misidentified as emerald — several famous 'emeralds' in European treasuries have turned out to be peridot from the Egyptian island of Zabargad.
Name origin
Uncertain, probably from an Arabic word for gem, by way of Old French. The mineral name olivine is separate and later, from the colour.
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
- Olivine — mineral · gem-quality olivine, and the iron that colours it is part of the essential composition rather than an impurity — which is why there is only one colour of peridot
contains
is commonly confused with
- Emerald — 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
- Emerald — 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
Sources
- Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
- Material WorldOur own writing