Demantoid Garnet (Cat's-Eye) | Gemopedia

The term cat's eye, or chatoyancy, is used to describe a phenomenal optical property in gemstones, in this case demantoid garnet. 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. Demantoid garnets that feature a cat's eye are rare.
Colors
Light To Dark Green To Yellow-Green

Demantoid Garnet (Cat's-Eye) Classification

Common Name

Demantoid Garnet (Cat's-Eye)

Species

Andradite

Variety

Cat's-Eye Demantoid Garnet

Colors

Light To Dark Green To Yellow-Green

Alternate Names

Gemstone Groups

Garnet

Key Separations

OTL RI, spectrum and SG

Comments

Demantoid Garnet (Cat's-Eye) Optical Properties

Transparency

Semitransparent To Opaque

Refractive Index

1.888-0

Birefringence

Optic Character

NA

Optic Sign

NA

Polariscope Reaction

Singly Refractive (SR) With ADR

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

None

Dispersion

Strength: strong fire Value: 0.57

Comments

Demantoid Garnet (Cat's-Eye) Chemistry & Crystallography

Chemical Name

calcium iron silicate

Chemical Formula

Ca3Fe2(SiO4)3

Synthesis

Crystal System

Cubic

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline to Aggregate

Comments

Demantoid Garnet (Cat's-Eye) Characteristic Physical Properties

Hardness

6.5-7

Streak

Specific Gravity

3.81-3.87 Typical: 3.84

Toughness

Poor

Inclusions

Cat's-eye demantoid garnet is type II clarity stone. Chatoyancy is caused by parallel needles. Due to the stones low mohs hardness it might have scratches and abrasions. Fibrous asbestos "horsetail inclusions" in Russian material. Stress fractures in Namibian stones.

Luster

SubAdamantine

Stability

Good

Fracture

Conchoidal, Uneven

Cleavage

None

Comments

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