Alexandrite (Cat's-Eye) | Gemopedia

The term cat's eye, or chatoyancy, is used to describe a phenomenal optical property in gemstones, in this case chrysoberyl. The effect, when present, appears as a bright, narrow slit similar to the pupils in the eyes of your favorite feline. This phenomenon is caused by parallel fibrous or needle-like inclusions that interfere with the passage of light throughout the crystal, scattering and reflecting light back to the viewer as a thin line. Chatoyant chrysoberyl is particularly incredible because it exhibits two rare phenomena: both the cat's eye effect and color change.
Colors
Daylight Yellowish, Brownish, Grayish, Blueish Green. Incandescent Light: Orangy, Brownish Red To Purple Red

Alexandrite (Cat's-Eye) Classification

Common Name

Alexandrite (Cat's-Eye)

Species

Chrysoberyl

Variety

Cat's-Eye Alexandrite

Colors

Daylight Yellowish, Brownish, Grayish, Blueish Green. Incandescent Light: Orangy, Brownish Red To Purple Red

Alternate Names

Gemstone Groups

Key Separations

Cat's-eye and color change, RI, SG and spectrum.

Comments

Alexandrite (Cat's-Eye) Optical Properties

Transparency

Semitransparent - Semitranslucent

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 to moderate red
LWUV: Inert to moderate red

CCF Reaction

red

Pleochroism

Trichroic, strong green, orange and purplish red

Dispersion

Strength: weak fire Value: 0.015

Comments

Alexandrite (Cat's-Eye) Chemistry & Crystallography

Chemical Name

beryllium aluminum oxide

Chemical Formula

BeAl2O4

Synthesis

Crystal System

Orthorhombic

Classification

Oxide

Nature

Natural

Crystallinity

Crystalline to Aggregate

Comments

Alexandrite (Cat's-Eye) Characteristic Physical Properties

Hardness

8.5

Streak

White

Specific Gravity

3.71-3.75 Typical:3.73

Toughness

Excellent

Inclusions

Natural cat's-eye alexandrite typically has fine needles or hollow tubes. The stones can have fluorite, apatite, mica platlets, rutile and multi-phase inclusions along with negative crystals, liquid and fingerprint inclusions. Some stones might show twinning.

Luster

SubAdamantine

Stability

Very Good

Fracture

Conchoidal

Cleavage

Good, in one direction, Poor, in two directions

Comments

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