Gem library
Tiger's eye
The quartz that follows the light
Tiger's eye was born from a remarkable chemical replacement: fibres of blue asbestos were gradually replaced by silica while keeping their perfect alignment. It is those fossil fibres that reflect light as a moving band — chatoyancy.
- Hardness (Mohs)
- 6.5 – 7
- Density
- 2.64 – 2.71
- Crystal system
- Trigonal
- Refractive index
- 1.534 – 1.540
- Cleavage
- None (fibrous structure)
Mineralogical identity
- Family
- Fibrous quartz — pseudomorph of crocidolite
- Species
- Quartz
- Variety
- Tiger's eye
- Chemical formula
- SiO₂ + iron oxides
- Crystal system
- Trigonal (fibrous aggregate)
- Classification
- Semi-precious stone
- Rarity
- Common
- Indicative price
- €0.50 – 6/ct
Etymology
Descriptive: the moving band of light evokes a big cat's pupil. The phenomenon is called chatoyancy, from the French chat, cat.
Physical & optical properties
- Hardness (Mohs)
- 6.5 – 7
- Density
- 2.64 – 2.71
- Refractive index
- 1.534 – 1.540
- Cleavage
- None (fibrous structure)
- Fracture
- Splintery
- Lustre
- Silky, chatoyant
- Diaphaneity
- Opaque
- UV fluorescence
- None
- Pleochroism
- None
- Colours
- golden brown, yellow, blue (hawk's eye), red (bull's eye)
Formation, geology & history
A spectacular pseudomorph
Originally the rock is crocidolite: a blue fibrous amphibole, known industrially as blue asbestos. Silica-bearing fluids circulating through fractures gradually dissolve the fibres and deposit quartz in their place, fibre by fibre, respecting their orientation. The result is a massive quartz whose internal structure consists of billions of parallel channels. When the crocidolite keeps its original blue, you get hawk's eye; when the iron oxidises to yellow-brown goethite, golden tiger's eye; heated, it turns mahogany red — bull's eye. Note: the finished stone contains no free asbestos and is entirely safe to handle.
Chatoyancy, how it works
The band of light appears perpendicular to the fibres and shifts as the stone or the light source moves. For it to be beautiful, the lapidary must orient the cabochon precisely: the dome must arch along the fibre axis, and the band must fall exactly in the centre. A poorly oriented cabochon gives a blurred, off-centre shimmer, which halves its value. The same optical principle governs the cat's eye of cymophane (chrysoberyl), infinitely rarer and dearer, where the effect comes from microscopic channels.
Market and deposits
The Griquatown deposit in South Africa has supplied most of the market since the nineteenth century and has made tiger's eye a very affordable stone — so abundant that it damaged its standing in fine jewellery. It is found in cabochons, beads, pebbles and turned objects. The prized pieces are those with a sharp, lively band and a deep honey colour, along with the rarer hawk's eyes of a clean blue-grey. The electric blue or green versions in shops are dyed.
How to recognise it
- The chatoyancy movesTilt the stone under a point light: the band must glide across the surface. A fixed, painted or printed band betrays an imitation.
- Visible fibrous structureOn an edge or in grazing light, tightly packed parallel fibres are visible. Fibre-optic glass (cat's eye glass) shows over-regular, geometric fibres.
- Hardness 7It scratches glass. A soft chatoyant stone is more likely satin spar (fibrous gypsum, hardness 2) or fibrous serpentine.
Imitations, treatments & confusions
- Fibre glass («synthetic cat's eye»)Drawn glass with parallel fibres, very common in beads. The chatoyancy is too perfect, too sharp, often multiple, and the glass warms quickly in the hand.
- Dyed tiger's eyeBright blue, green or purple versions are always coloured. Natural hawk's eye is a muted blue-grey, never electric.
- Serpentine or fibrous gypsumPossible confusion on silky-sheened stones, but their hardness (3 to 5) means a knife — or even a fingernail for gypsum — scratches them.
Deposits & origins
South Africa (Northern Cape, the historic Griquatown deposit that dominates the world market), Western Australia, Namibia, Burma, India, Brazil, China
Care & precautions
- Brief rinsing in warm soapy water; avoid long soaking, which can dull the fibres.
- No salt, no acids: they attack the iron oxides between the fibres.
- Avoid ultrasonic cleaners: vibration can loosen the fibrous structure and matt the polish.
- Sunlight does not affect it; a gentle cloth polish restores its silky sheen.
Traditions & crystal healing
- Chakras
- Solar plexus · root
- Zodiac signs
- Leo · Capricorn · Gemini
- Element
- Fire · Earth
A stone of protection and discernment in tradition: the open eye that sees things coming. It is credited with clear-headed courage, confidence in one's own decisions and help against scattered attention. Romans wore it engraved as an amulet before battle — one of the few directly documented ancient uses.
The virtues described here belong to tradition and cultural heritage. They are in no way medical advice and never replace a consultation.
Frequently asked questions
Does tiger's eye contain asbestos?
No. The original asbestos fibres were entirely replaced by silica during pseudomorphism. The finished, polished stone is harmless.
Tiger's, hawk's or bull's eye?
Same stone, three states of iron: blue-grey (hawk, unoxidised iron), golden brown (tiger, iron oxidised to goethite), mahogany red (bull, usually obtained by heating).
Why does my cabochon have no fine band?
A matter of cutting orientation: the fibres must be parallel to the cabochon base with the dome centred on them. Rough cutting gives a blurred shimmer.