Cat's Eye Opal Identification Guide

What Cat's Eye Opal Looks Like

Cat's Eye Opal is opal (hydrated silica) that displays a single sharp band of light, chatoyancy, across a polished cabochon. The effect comes from parallel fibrous inclusions or oriented channels within the opal. Body colors are usually honey, yellow, green, white, or pinkish, often translucent to semi-transparent. Most cat's eye opal is common opal (no play-of-color), though rare stones combine a moving eye with flashes of spectral color. The luster is waxy to glassy.

Key Visual Traits

• A single straight light band that floats across the dome
• Soft, often milky or honey translucency
• Waxy to vitreous luster, no metallic sheen
• Warm, lightweight feel

Step-by-Step Field-ID Checklist

1. Rotate under a single light. Look for one crisp band that moves; this is chatoyancy, not the broad colored fire of precious opal.
2. Distinguish from play-of-color. Precious opal shows shifting patches of red, green, and blue; cat's eye is a single silvery or colored stripe.
3. Test hardness. Opal is soft, about 5.5 to 6.5, so quartz scratches it easily.
4. Weigh it. Specific gravity is low (1.98 to 2.25), noticeably lighter than quartz or chrysoberyl of the same size.
5. Inspect translucency. Most cat's eye opal glows when backlit.
6. Avoid harsh tests. Opal can craze and crack; do not heat it.

Diagnostic Tests

• Hardness: 5.5 to 6.5 (softer than quartz).
• Fracture: Conchoidal, brittle.
• Streak: White.
• Density: Very low, about 2.0 to 2.2; the lightest of common cat's eye gems.
• Acid/magnetism: Inert and non-magnetic.
• UV: Some opal fluoresces greenish or white.

Common Look-Alikes and How to Tell Them Apart

• Cat's Eye Chrysoberyl: Much harder (8.5) and much denser; the eye is razor-sharp with a bright "milk and honey" effect. Opal is soft, light, and its eye is gentler.
• Cat's Eye Quartz: Harder (7) and heavier; cannot be scratched by a knife, whereas opal can.
• Cat's Eye Apatite or Tourmaline: Both are harder and denser; tourmaline shows strong color zoning, apatite is brittle but scratches harder than opal.
• Moonstone: Shows a billowy blue sheen (adularescence) that fills the dome, not a single sharp line.
• Fiber-optic glass simulant: Perfectly even eye with a visible grid; true opal is hydrated silica that often shows internal play or a milky glow.

Where It Is Typically Found

Cat's eye common opal comes mainly from Tanzania (notably Tanzanian "moss" and honey opals), Madagascar, Brazil, and the western United States. Honey to greenish chatoyant opal from East Africa is the most frequently encountered in the trade. Because opal is delicate, field specimens are often found as waterworn nodules in volcanic or sedimentary host rock.

Collector and Field Notes

Handle cat's eye opal gently; opal can craze (develop fine internal cracks) if dried too fast or heated, so never use a hot point or thermal test on it. The eye is sharpest when the cabochon is cut with the fibers running straight across the dome, and a well-centered band greatly raises value. East African honey and greenish material is the most common in the trade, while bodies that combine chatoyancy with true play-of-color are genuinely rare and prized. Store it away from direct heat and harsh light, and clean only with a soft, damp cloth rather than ultrasonic or steam cleaners, which can damage porous opal.