Tigers Eye Properties, Facts and Photos

What is Tigers Eye?

Tigers eye (or tiger eye) is a yellow and brown variety of quartz known for being chatoyant.

Chatoyancy, or chatoyance, is an optical phenomenon found in a few minerals but is relatively rare compared to other optical phenomena.

characteristic silky sheen.

The extent to which this can be seen depends on the orientation of the fibres and the stone cutter's skill.

Chatoyant gemstones tend to be cut as cabochons because the domed shape enhances the phenomenon.  

When a chatoyant tigers eye stone is gently moved, the band of light also moves, creating the illusion that colours and patterns are moving.

The word 'chatoyant' comes from French for 'cat's eye.'

Tigers eye is a relatively hard stone, which makes it easy to work with. On the Mohs scale of hardness, it grades 7. The Mohs scale measures the resistance of one mineral when scratched by another.

Huge reserves of tigers eye can be found in Western Australia, an area rich in iron. South Africa also has vast reserves. The finest-grade tigers eye comes from Griqualand West in the Northern Cape.

When tigers eye is heated, it changes colour. The brown variety, which is the most popular, is the stone people tend to be familiar with. Red tigers eye eye and black tigers eye are produced through heat-treatments.

Heat treatments have been used for thousands of years to enhance or change the colour of rocks and minerals. Ancient Roman author, naturalist and philosopher Pliny the Elder documented the effects of fire on stones. He wrote, "One gemstone could be changed into another" and "The colour of quartz could be changed to that of an emerald."

In chapter 75 of his encyclopaedia, Naturalis Historia, Pliny writes;

There is considerable difficulty in distinguishing genuine stones from false; the more so, as there has been discovered a method of transforming genuine stones of one kind into false stones of another.

Sardonyx, for example, is imitated by cementing together three other precious stones, in such a way that no skill can detect the fraud; a black stone being used for the purpose, a white stone, and one of a vermilion colour, each of them, in its own way, a stone of high repute.

Nay, even more than this, there are books in existence, the authors of which I forbear to name, which give instructions how to stain crystal in such a way as to imitate smaragdus and other transparent stones, how to make sardonyx of sarda, and other gems in a similar manner. Indeed, there is no kind of fraud practised, by which larger profits are made.

Ref: (Pliny's Naturalis Historia chapter 75) Please Note.

Smaragdus is an ancient name for emerald. Sardonyx and sard are both types of carnelian.

The Association of Tigers Eye with Asbestos

There is some concern regarding the presence of asbestos in tigers eye.

Until quite recently, it was widely believed that the crocidolite, a type of asbestos, had been replaced with silicon dioxide over millions of years.

In geology, when one mineral replaces another, the process is known as pseudomorphism. A pseudomorph looks like one mineral but is actually another. Although the shape or crystal structure of the original mineral remains the same, the mineral itself has changed. A new mineral replaces the original one.

Pseudomorph literally means 'false form'.
Although it had long been believed that the asbestos in tigers eye had been replaced with quartz, a study carried out in 2003 revealed no mineral replacement has taken place. Tigers eye is made up of crocidolite and quartz.

Many articles still claim the crocidolite has been replaced with quartz, but this in-depth study concludes otherwise. 

The thought of asbestos being present in tigers eye often causes concern, but the danger from this mineral comes from inhaling its dust or fibres. In tigers eye, the crocidolite is locked deep within the quartz, so poses no risk.

Asbestos was widely used on an industrial scale until the year 2000. It only becomes dangerous when microscopic fibres break away, become airborne and are breathed in. That's simply not possible when handling a tigers eye stone because the asbestos fibres are encapsulated within the quartz.

It's worth noting that malachite is an ore of copper so its dust is highly toxic. The microscopic crystalline silica particles in the mineral quartz are also dangerous if inhaled. Silicosis is a serious lung disease caused by inhaling these fine particles.

In fact, the dust or fibres from many minerals can be hazardous, but that doesn't mean they're dangerous to handle. They only become a health hazard when being cut, sanded or drilled.

Chatoyance in tigers eye is caused as light reflects off the crocidolite fibres. Please Note.

Blue Tigers Eye - Good to Know

Blue tigers eye is also known as Hawks Eye and Falcons Eye, although the latter is not used as often.

In brown tigers eye, the crocidolite fibres gradually oxidise and break down. During this process, they transform into limonite, an iron oxide mineral. The limonite produces the stone’s characteristic colour and chatoyant effect.

In blue tigers eye, the crocidolite fibres remain less oxidised, preserving their bluish-grey colour. The blue hue comes from the iron content in the crocidolite, which differs slightly from the iron in the brown variety.

'Oxidised' refers to a process where a substance reacts with oxygen, often leading to a change in its chemical composition or appearance. For example, when an apple is peeled and left to sit, it turns brown as it oxidises.

Although tigers eye can have a natural red hue, most red tigers eye, also known as 'bulls eye', is heat-treated. During this process, the yellow limonite converts to red hematite, giving the stone a deep red colour.

Red tigers eye does not exhibit chatoyance because the natural fibrous structure of the quartz alters during the heat treatment, which affects the light-scattering properties responsible for this effect.

Article Photos

The photos of tigers eye in our article, including the red and black tigers eye in the pop-up photos, are from our collection.

The goethite pseudomorph after pyrite in our second photo is courtesy of Stan Celestian. The image is clickable and redirects to the original photo.