Tiger's Eye
Tiger’s eye owes its appearance to a process called pseudomorphic replacement, which is a more interesting story than “banded brown quartz” suggests. It began as a fibrous, asbestos-like mineral — typically crocidolite or riebeckite — and silica gradually replaced that mineral fiber by fiber, preserving the original parallel fibrous structure while swapping out the underlying chemistry entirely. What’s left is quartz, chemically and in hardness, but with a microscopic fibrous architecture quartz wouldn’t normally have on its own.
That inherited structure is what produces chatoyancy: a tight, silky band of reflected light that appears to move across the stone as it’s turned, the same optical effect that gives cat’s-eye chrysoberyl its name, though the underlying cause is different in each case. In tiger’s eye, the effect runs in golden-brown to reddish-brown bands, which is where the name comes from. Blue-gray material with the same structure but less iron oxidation is sometimes sold separately as “hawk’s eye.”
Because it’s genuinely quartz, tiger’s eye shares quartz’s Mohs 7 hardness and SiO2 chemistry — durable enough for everyday jewelry, more resistant to scratching than most of the softer ornamental stones it’s often displayed alongside. South Africa’s Northern Cape Province is the best-known modern source, with additional material coming from Australia, India, Myanmar, and the United States.
Tiger’s eye doesn’t appear on any of the historical or modern monthly birthstone lists, or on either zodiac system, tracked on this site — it’s included here as a standalone reference entry rather than as part of a birthstone system comparison, the same way malachite and larimar are.
Gemmological properties
| Mohs hardness | 7 |
|---|---|
| Crystal system | Trigonal |
| Chemical formula | SiO2 |
| Refractive index | 1.544–1.553 |
| Color family | Brown, Yellow, Orange |
| Variety of | quartz |
| Also known as | — |
| Origins | South Africa, Australia, India, Myanmar, United States |
| Organic material | No |
Tiger's eye is chatoyant quartz: silica has replaced a fibrous asbestiform mineral (crocidolite/riebeckite) fiber for fiber, preserving its parallel structure and producing the silky, moving band of light (chatoyancy) the stone is named for. Its hardness and formula are quartz's, not the original fiber mineral's.
Frequently asked questions
- Is tiger's eye a type of quartz?
- Yes. It's chatoyant quartz — quartz at Mohs 7, the same hardness and chemical formula (SiO2) as amethyst, citrine, and rock crystal. What makes it look different is a pseudomorphic replacement process, not a different mineral.
- What causes the moving band of light in tiger's eye?
- The effect is called chatoyancy. It happens because the stone contains microscopic parallel fibers — remnants of an asbestiform mineral that silica gradually replaced while preserving its fibrous structure — that reflect light in a tight, moving band as the stone or the light source turns.
- Is tiger's eye a birthstone on any of the lists this site tracks?
- No. It doesn't appear on any of the historical, US, UK, or zodiac systems documented on this site — it's covered here purely as a gemstone reference entry.