Tiger's eye

Tiger's eye
Polished tiger's eye gemstone
General
Category	Mineral
Formula (repeating unit)	Silica (silicon dioxide, SiO2)
Identification
Colour	golden to red-brown
Mohs scale hardness	5.5 - 6
Luster	Silky
Specific gravity	2.64 – 2.71

Tiger's eye (also called tiger eye) is a chatoyant gemstone that is usually a metamorphic rock that is a golden to red-brown colour, with a silky lustre. Members of the quartz group, Tiger's eye and the related blue-coloured mineral Hawk's eye gain their silky, lustrous appearance from the parallel intergrowth of quartz crystals and altered amphibole fibres that have mostly turned into limonite.

The gems are usually cut en cabochon in order to best display their chatoyancy. Red stones are brought about through gentle heat treatment. Dark stones have had their colours improved and been artificially lightened using nitric acid treatments.

Honey-colored stones have been used to imitate the much higher valued cat's eye chrysoberyl (cymophane), but the overall effect is unconvincing. Artificial fibre optic glass is a common imitation of tiger's eye, and is produced in a wide range of colours. Tiger's eye comes primarily from South Africa and east Asia.

Tiger iron is an altered rock composed chiefly of tiger's eye, red jasper and black hematite. The undulating, contrasting bands of colour and lustre make for an attractive motif, and it is mainly used for jewellery-making and ornamentation. Tiger iron is a popular ornamental material used in a variety of applications, from beads to knife hilts.

Tiger iron is mined primarily in South Africa and Western Australia. Tiger's eye is composed chiefly of silicon dioxide (SiO₂) and is coloured mainly by iron oxide. The specific gravity ranges from 2.64 to 2.71. It is formed by the alteration of crocidolite.