Jewellers' Network

Inclusions – African Gemmological Laboratory

Inclusions African Gemmological Laboratory

In gemmology an inclusion is a clarity characteristic, enclosed within a gemstone, or breaking the surface from the interior.

Inclusions are normally perceived as being a negative feature in a gem as they usually devalue a stone, except in the case of ‘horsetail’ inclusions in demantoid garnets and phenomenal gems where the inclusions cause the phenomena.


These long thin needle like inclusions are normally minerals trapped within the host, but they could also be hollow growth tubes, a defect formed during the crystals growth.


Often fluids are trapped within a gemstone whilst it is forming.

These fluid inclusions may be fine hair like inclusions called trichites as is often seen in tourmaline. When the fluid cools it may release a gas bubble, making it a ‘two phase’ inclusion.

Occasionally a solid will form as the liquid and gas cool, this would be called a ‘three phase’ inclusion and is often seen in emerald.


Clouds are normally a mass of tiny impurities or microscopic crystals, this can make the stone appear ‘milky’. Clouds
are often seen in diamonds from Zimbabwe.

Crystals and Mineral Inclusions

Crystals and other minerals can be enveloped by a crystal as it grows or they can form within the host if the conditions are right. It is not uncommon to have crystals of the same material trapped within a larger host, in diamonds this is referred to as a ‘knot’.