Tiger's eye: meaning, properties and lore

The mineral

The fibrous mineral is crocidolite, the blue asbestiform variety of the sodic amphibole riebeckite, and it filled fractures in the host rock. Gemological Institute of America describes the stone as a quartz pseudomorph after crocidolite, a description that places the blue amphibole at the centre of its structure.¹²

Riebeckite, the amphibole linked to the crocidolite in tiger's eye, has the formula Na2Fe5Si8O22(OH)2. Tiger's eye has a Mohs hardness of 8.5, which places it among the harder gem materials used in jewellery and carving. These two measured values are the core facts for identifying the stone.²³

The golden colour comes from iron oxides trapped by the quartz. The dark brown needles within the stone are iron oxide and hydroxide formed from weathered amphibole. Where crocidolite is broken down by oxidizing fluids, it turns into hematite and goethite, which accounts for the variation in tone across a polished piece.¹²⁴

Chatoyancy, the silky band of light that moves across a polished surface, is caused by light reflecting off aligned needle-like inclusions within the stone. The soft golden-brown sheen comes from parallel fibres of crocidolite. Gemological Institute of America notes that the stone shows a mosaic of fibrous crocidolite bundles on end in cross section, encased within quartz.¹⁵⁴

The stone is structurally distinct from pietersite, a brecciated variety made of chalcedony, while tiger's eye is made of columnar quartz. Tiger's eye is formed when crocidolite and columnar quartz grow simultaneously from opposing crack walls toward the centre of a vein during a crack-seal process. Its fibres lie parallel in longitudinal section, with crocidolite encased within columnar quartz.²⁴

Gemological Institute of America records the Pilbara region of Western Australia as the rock source of tiger's eye. A polished slab from the Marra Mamba Iron Formation of Western Australia is also shown in the institute's collection. The host rock formed from iron-rich sediments deposited in ancient seas about two and a half billion years ago. The stone is commonly polished into beads and large cabochons.¹

History and lore

Wibel (1873) recorded that tiger's-eye has long been attributed to pseudomorphism with quartz replacing crocidolite. The stone was therefore understood as a replacement of one mineral by another, a view that shaped how it was described for decades.²

The Curious Lore of Precious Stones lists crocidolite in its index, with the entry giving the alternative spelling Krokidolite. The index entry places the mineral among the stones discussed in that work.⁶

Birthstone and zodiac links

Crystal practitioners list tiger's eye as the modern planetary stone for Gemini, from May 21 to June 20. This modern zodiac link is a modern practitioner link rather than an ancient one.

Tiger's eye is the accepted gem for the 9th wedding anniversary, according to crystal practitioners. This anniversary link is a modern practitioner link, and it is not a historical custom.

What crystal practitioners say

Crystal practitioners associate tiger's eye with the mind and personal growth. They say it deals with self-worth, self-criticism and blocked creativity. They describe it as excellent for people who are spaced out or uncommitted.

Tiger's eye is said to facilitate correct use of power, support integrity and assist in accomplishing goals, according to crystal practitioners. Believers hold that the stone guides how a person uses influence in daily affairs. The same practitioners link it to a steady, principled approach to work.

Tiger's eye is believed to assist in achieving clarity and aid running a successful business, according to crystal practitioners. Advocates describe it as a stone for people who manage their own enterprises. This business use is their view and is not a finding from testing.

What testing has found

Heaney and Fisher (2003) proposed that quartz and riebeckite grew synchronously through an episodic crack-seal mechanism rather than by pseudomorphism. Their proposal set aside the older view that the stone was a replacement of one mineral by another.²

Heaney and Fisher found that optical and electron microscopic observations failed to show any evidence for pseudomorphism in tiger's-eye. Gemological Institute of America reports that standard gemological properties cannot separate tiger's-eye from petrified tree fern, which has caused confusion in the jewelry market.²⁴

Glass can be made to look like tiger's eye, and it is one of several materials used to imitate the stone. The jewelry industry uses the word simulant for such materials, which look like another gem but differ in chemical composition and crystal structure.³