Gems are often only available in one colour.
The array of beautiful colours we see in natural gemstones can be created by one of three events:
Firstly, and most commonly, gems coloured by the presence of impurities are known as allochromatic (“allo” meaning other). Garnet and Beryl are two examples.
To a lesser extent, the colour seen in a few gemstones can be caused by optical properties within the gem and its reflection from, or just under, its surface, examples being Moonstone and Opals. These gems are known as pseudochromatic.
Finally it can be due to the inherent chemical makeup of the crystal; these gems are known as idiochromatic (“idio” meaning inherent).
An idiochromatic gem is one where the colour is not due to impurities, but where the colouring element is an essential part of its chemical formula. Iron in Peridot for example is what provides the gem with its vibrant green colour and it is also an essential part of the gem’s construction.
If a gemstone is only available in one colour such as Peridot, Malachite and Azurite, then it is a strong indication that the gem is idiochromatic
