Chrysoberyl (Cat's-Eye) | Gemopedia

The term cat's eye is used to describe a phenomenal optical property in gemstones, but in this case, chrysoberyl. Known as chatoyancy, this effect appears as a bright, narrow slit--similar to the pupils in the eyes of your favorite feline. This phenomenon is caused by the presence of parallel fibrous or needle-like inclusions that interfere with the passage of light through the crystal, scattering and reflecting light back to the viewer as a thin line.
Alternate
Names
Cymophane, Cat's-Eye
Colors
Yellow To Yellowish Green, Grayish Green, Brown To Brownish Yellow

Chrysoberyl (Cat's-Eye) Classification

Common Name

Chrysoberyl (Cat's-Eye)

Species

Chrysoberyl

Variety

Cat's-Eye Chrysoberyl

Colors

Yellow To Yellowish Green, Grayish Green, Brown To Brownish Yellow

Alternate Names

Cymophane, Cat's-Eye

Gemstone Groups

Key Separations

refractive index, specific gravity, appearance and spectrum. Spectrum should reflect a strong diagnostic band at 444nm.

Comments

Phenomenal chrysoberyl may exhibit chatoyancy, in which case it is classified as "cat's-eye chrysoberyl." Cymophane will show a broad sheen instead of a distinct cat's-eye. Most often seen with yellowish green to orangy yellow background with strong silvery white cat's-eye.Cat's-eye chrysoberyl is the only chatoyant stone allowed to be called by only the name cat's-eye. Rare stones might show 4 rayed stars.

Chrysoberyl (Cat's-Eye) Optical Properties

Transparency

Semitransparent - Translucent

Refractive Index

1.746-1.755
Tolerance:(+0.004/-0.006)

Birefringence

0.008-0.01

Optic Character

Biaxial

Optic Sign

Positive

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

Unobservable

Dispersion

Strength: weak fire Value: 0.015

Comments

Chrysoberyl (Cat's-Eye) Chemistry & Crystallography

Chemical Name

beryllium aluminum oxide

Chemical Formula

BeAl2O4

Synthesis

Crystal System

Orthorhombic

Classification

Oxide

Nature

Natural

Crystallinity

Crystalline

Comments

Chrysoberyl (Cat's-Eye) Characteristic Physical Properties

Hardness

8.5

Streak

White

Specific Gravity

3.71-3.75 Range:+/-0.02 Typical:3.73

Toughness

Varies

Inclusions

Cat's-eye chrysoberyl will have parallel rutile needles or hollow growth tubes parallel to the c-axis that have give the appearance of silk. Stone can contain fingerprints or liquid inclusions and have angular included crystals. Stone might show twinning

Luster

Bright Vitreous

Stability

Very Good

Fracture

Conchoidal

Cleavage

Good, in one direction, Poor, in two directions

Comments

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