Cat's-Eye Demantiod Garnet | Gemopedia

Demantoid is named for its diamond-like luster and is a variety of andradite garnet. One of the most distinctive features of demantoid is the presence of characteristic inclusions known as horsetails. The effect is caused by the presence of wispy, hair-like inclusions of byssolite. Demantoids containing well-formed horsetails are highly prized by collectors, and generally command a premium. Demantoid gemstones that feature the Cat's Eye, or Chatoyant optical effect are rare.

Cat's-Eye Demantiod Garnet Classification

Common Name

Cat's-Eye Demantiod Garnet

Species

Andradite

Variety

Cat's-Eye Demantiod Garnet

Colors

light to dark green to yellow-green

Alternate Names

Gemstone Groups

Group: Garnet

Key Separations

OTL RI, spectrum and SG

Comments

Cat's-Eye Demantiod Garnet Optical Properties

Transparency

Semitransparent To Opaque

Refractive Index

1.888-0

Birefringence

Optic Character

NA

Optic Sign

NA

Polariscope Reaction

singly refractive, commonly with ADR (SR-ADR)

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

Dispersion

Strength: strong fire Value: 0.57

Cat's-Eye Demantiod Garnet Chemistry & Crystallography

Chemical Name

calcium iron silicate

Chemical Formula

Ca3Fe2(SiO4)3

Synthesis

Crystal System

Cubic

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline To Aggregate

Cat's-Eye Demantiod Garnet Characteristic Physical Properties

Hardness

6.5 to 7

Streak

Specific Gravity

3.81-3.87 Typical: 3.84

Toughness

Poor

Inclusions

Cat's-eye demantiod 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 To Vitreous

Stability

Good

Fracture

Conchoidal To Uneven

Cleavage

None, Sometimes Distinct Parting

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