Cat's Eye Chrysoberyl
Last updated: April 2026
Cat's eye chrysoberyl (cymophane) chatoyancy is caused by parallel growth tubes or rutile needles aligned along the crystallographic c-axis. The 'milk and honey' effect — one side appearing white, the other gold under a point light — is a field diagnostic rarely seen in other chatoyant gems. Always cut as a cabochon. Sources include Sri Lanka, Brazil, India, Zimbabwe, and Russia. No commercial synthetic exists; separation from simulants uses RI.
Cat's Eye Chrysoberyl has a specific gravity of 3.73 and a refractive index of 1.746–1.755, with a Mohs hardness of 8.5. It is biaxial +.
Physical & Optical Properties
Measured with a polariscope, a refractometer, a hydrostatic balance, a Chelsea filter, a UV torch, a loupe, a darkfield loupe and a spectroscope — step-by-step for each.
Through the refractometer
Drawn from the refractive index above, on a 1.40–1.81 scale. How to take this reading.
Related: Chrysoberyl Varieties
Key Differentiators
- 'Milk and honey' effect: tilting the stone under a single point light reveals one half whitish ('milk') and one half gold/yellow ('honey') — unique to chrysoberyl among chatoyant gems
- High RI 1.746–1.755 — highest of any commercially significant chatoyant gem; definitive against all simulants
- High SG 3.70–3.78 — noticeably heavy for its size; all simulants are lighter
- Hardness 8.5 — no surface scratches from quartz or steel; harder than all simulants
- Single bright, sharp chatoyant band that moves smoothly as the stone is rotated under a point light
- No commercial synthetic exists — concern is simulant separation only
Natural vs. Synthetic
Synthetic cat's eye chrysoberyl is commercially available (Czochralski (pulled), Hydrothermal). Distinguishing natural from synthetic typically requires microscopic examination of internal features.
- General Note: No commercial synthetic cat's eye chrysoberyl exists. All cat's eye chrysoberyl on the market is natural. Chatoyancy is caused by parallel growth tubes or silk inclusions aligned along the c-axis. Synthetic: No known synthetic. The primary concern is simulants — fiber-optic glass is the most common substitute. High RI (1.746–1.755) and SG (3.73) are definitive against all simulants.
- Refractometer: RI 1.746–1.755 (biaxial positive). This is the highest RI of any chatoyant gem encountered commercially. Synthetic: Fiber-optic glass: RI ~1.52 (isotropic). Apatite cat's eye: RI 1.634–1.638. Quartz cat's eye: RI 1.544–1.553. Scapolite cat's eye: RI 1.550–1.572. Tourmaline cat's eye: RI 1.624–1.644. All are conclusively lower.
- Specific Gravity: SG 3.70–3.78 (typical 3.73). Heavy for its size — will sink quickly in methylene iodide (SG 3.33). Synthetic: Fiber-optic glass SG ~2.6. Apatite SG 3.18. Quartz SG 2.65. Scapolite SG 2.65. All float or are noticeably lighter.
Loupewise Pro includes a two-phase natural vs. synthetic testing protocol for Cat's Eye Chrysoberyl.
Common Simulants
- Fiber-optic glass (glass cat's eye): Most common simulant. Isotropic, RI ~1.52, SG ~2.6 (much lighter). Band often too uniform and narrow. Under darkfield: gas bubbles and curved flow lines. No milk-and-honey effect — the band stays the same color when stone is tilted. RI test separates cleanly.
- Apatite cat's eye: Similar honey-yellow color. RI 1.634–1.638 (lower). SG 3.18 (lighter). Hardness only 5 — scratched easily by a penknife. Uniaxial negative. Less pronounced milk-and-honey effect.
- Quartz cat's eye: Very common and inexpensive. RI 1.544–1.553 (much lower). SG 2.65 (noticeably lighter). Band typically less sharp. No milk-and-honey effect. Uniaxial positive.
- Tourmaline cat's eye: RI 1.624–1.644 (lower). SG 3.06 (lighter). Strong pleochroism visible when rotating stone. Band less sharp than chrysoberyl. Uniaxial negative with strong birefringence.
- Scapolite cat's eye: RI 1.550–1.572 (much lower). SG 2.65 (much lighter). Uniaxial negative. Rarely encountered; band quality typically inferior to chrysoberyl.
Treatments
- Dyeing (rare)
- Irradiation (rare — color modification)
Measurement Guides
Identifying a cat's eye chrysoberyl? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Cat's Eye Chrysoberyl is one of the 132 species in Loupewise’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
Practice exams →