Tiger's eye — liquid light in stone
Tiger's eye — quartz that replaced silky crocidolite fibers and preserved their parallelism as microscopic "silk." When cut correctly, light focuses into a moving band — a feline flash called chatoyancy. Honey to bronze shades come from iron oxides; more blue — Hawk's eye, and tones can deepen to reds — Bull's eye.
Identity and names 🔎
Quartz with a "cat's eye" signature
Tiger's eye is a pseudomorph: quartz (SiO₂) replaces fibrous crocidolite, preserving its parallel structure. This microfibrous fabric generates the chatoyancy band.
Family and varieties
Hawk's eye — an earlier, bluish-gray stage (less iron spotting). Bull's eye is often produced by heating, enhancing red / burgundy tones. "Tiger iron" — layers of tiger's eye, hematite, and jasper.
How it forms 🧭
Three-step story
1) Crocidolite grows as blue, silky fibers in iron-rich rocks. 2) Silica-rich solutions infiltrate and replace fibers with quartz, preserving their orientation. 3) Iron oxides/hydroxides color the quartz golden brown.
Why the "eye" moves
Parallel-arranged microfibers act as cylindrical reflectors. The bright band runs perpendicular to the fibers and moves when the stone or light is turned.
From blue to gold to red
Preserved iron state → Hawk's eye (blue). Oxidized state → Tiger's eye (golden). Natural or applied heating can deepen to Bull's eye (red).
Imagine a silky band fossilized in quartz — tilt it, and the band comes alive with a flash.
Palette and pattern dictionary 🎨
Palette
- Golden "honey" — classic warmth.
- Bronze brown — contrasting bands.
- Bluish gray — Hawk's eye.
- Red / burgundy — Bull's eye (often heat treated).
Luster silky to vitreous. Quality pieces show a sharp, focused "eye" with minimal "flicker".
Pattern words
- Striped ("ribbon") — straight, parallel bands with one bright "eye".
- Feathery — slightly wavy fibers, softer luster.
- Brecciated — broken and re-cemented fragments (e.g., pietersite).
- Layered — tiger's eye alternated with hematite / jasper (tiger iron).
Observation tip: Use a single narrow light source. Rotate until the band "turns on"; leave the reflection slightly off-center to show movement.
Physical and optical details 🧪
| Property | Typical range / note |
|---|---|
| Chemical composition | SiO₂ (quartz), replacing crocidolite; golden color is given by iron oxides / hydroxides. |
| Crystal system / group | Trigonal • quartz (micro- / cryptocrystalline aggregate) |
| Hardness (Mohs) | 7 |
| Specific gravity | ~2.64–2.71 (varies with iron content) |
| Refractive index / optics | ~1.544–1.553; birefringence ~0.009; aggregates may show ~1.54 by spot measurement. |
| Pleochroism | None (color effects are reflective) |
| Luster / transparency | Silky to glassy; opaque to translucent at edges |
| Chipping / fracture | No cleavage; conchoidal fracture |
| Phenomenon | Chatoyancy (moving "eye") from parallel microfibers |
| Fluorescence | Usually unreactive |
| Treatments | Heating to red "bull's eye"; dying for unusual shades (green, bright blue). Record treatment status in documentation. |
Under the magnifier 🔬
Parallel "silk"
Expect parallel microfibers / subgrains; the "eye" runs across them. In brecciated varieties, fibers between fragments twist, causing "eyes" to swirl.
Color sources
Golden browns — from goethite / limonite spotting; blue tones — from residual chrysotile; reds often show subtle heating signs at edges under magnification.
Signs of treatment
In dyed pieces, color concentrates in pairs / around holes; in heat-treated reddened material, there may be slight surface interference and deeper burgundy zones.
Similar and imitations 🕵️
"Cat's eye" chrysoberyl
Sharper, brighter "eye" in single-color gems; significantly higher SG (~3.73) and RI (~1.74).
"Cat's eye" quartz
Quartz characterized by chatoyancy with rutile/fibrous inclusions; lacks the bands typical of tiger's eye and shows different colors.
Fiber optic glass
Very uniform "eye" that easily "slides"; no natural banding, smaller "mass" and visible glassy bubbles/flow lines at 10×.
Bronzite / hypersthene
Bronze schiller, not a sharp moving band; different chemistry (pyroxenes) and optics.
Quick checklist
- Golden brown bands with a moving band?
- Spot RI ~1.54, SG ~2.65, conchoidal fractures?
- Naturally somewhat uneven banding (not "factory" uniform)? → Likely tiger's eye.
Localities and uses 📍
Where found
South Africa (Northern Cape) — classic golden material; other sources: Western Australia, Namibia (especially pietersite), and India. "Tiger iron" is especially associated with South Africa and Australia.
What is made
Cabochons oriented to the central "eye", beads continuing the bands, inlays for geometric patterns, and sculptural pieces emphasizing banding.
Care, jewelry, and processing 🧼💎
Daily care
- Clean with lukewarm water + mild soap; dry with a soft cloth.
- Avoid ultrasound/steam on dyed or cracked pieces.
- Keep separate from harder gems to protect the polish.
Jewelry guidelines
- Suitable for rings, pendants, bracelets.
- Orient so that the "eye" is bright at the usual viewing angle.
- In bead necklaces, aim for matching band flow.
On the grinding wheel
- Cut with fibers parallel to the base plane so that the "eye" is maximal.
- Light pressure; cool. Pre-polish 600→1200→3k; finish with cerium oxide or aluminum oxide on leather / felt.
- In the case of Pietersite, stabilize cracks if needed and mark this.
Practical demonstrations 🔍
Find the “eye”
Use a single point light source and rock the stone until the band “locks in”. Mark the orientation for photography or study.
Band map
Place paper under the cabochon and draw the fiber / band direction — this way you'll see why the “eye” moves exactly like that.
Golden bands, moving light — tiger's eye shows how microstructure shapes optics.
Questions ❓
Is tiger's eye asbestos?
Its precursor is an asbestos mineral, but the final stones are replaced with quartz. Considered safe for normal wear; stone processors should manage silica dust exposure.
Is red tiger's eye natural?
Sometimes yes, but many red / burgundy stones are heated. The treatment status should be disclosed.
Why does the band look “fluffy”?
Wavy or mixed fiber directions soften the “eye,” giving a broader silky glow.
How to distinguish from imitations?
Fiber optic glass has a uniform “eye” and glassy bubbles / flow lines at 10×. Natural tiger's eye has a striped, somewhat uneven pattern and characteristic quartz features.
Metaphysics note
Often associated with grounding, attention, and focus. (Cultural / subjective use; not a substitute for professional care.)