Scapolite (Cat's-Eye) | Gemopedia

The term cat's eye, or chatoyancy, is used to describe a phenomenal optical property in gemstones, in this case scapolite. 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. Gem quality scapolite is rare and highly treasured by gem collectors, particularly when exhibits chatoyancy.
Colors
White, Pink, Violet, Yellow, Reddish Brown, Brown

Scapolite (Cat's-Eye) Classification

Common Name

Scapolite (Cat's-Eye)

Species

Scapolite

Variety

Cat's-Eye Scapolite

Colors

White, Pink, Violet, Yellow, Reddish Brown, Brown

Alternate Names

Gemstone Groups

Scapolite

Key Separations

RI, birefringence, optic character and possible fluorescence. Use birefringence blink method on reddish brown material to separate from cat's-eye beryl.

Comments

RI in reddish brown material is usually between 1.560 to 1.585 and birefringence is around 0.025Birefringence typically 0.004 to 0.020 but it increases as the stones RI increases.

Scapolite (Cat's-Eye) Optical Properties

Transparency

Semitransparent - Opaque

Refractive Index

1.55-1.585
Tolerance:(+0.015/-0.014)

Birefringence

0.004-0.037

Optic Character

Uniaxial

Optic Sign

Negative

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV:
LWUV:

CCF Reaction

Pleochroism

Unobservable

Dispersion

Comments

Scapolite (Cat's-Eye) Chemistry & Crystallography

Chemical Name

sodium or calcium aluminum silicate carbonate chloride

Chemical Formula

Na4Al3Si9O24Cl to Ca4Al6Si6O24(CO3, SO4)

Synthesis

Crystal System

Tetragonal

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline to Aggregate

Comments

Scapolite (Cat's-Eye) Characteristic Physical Properties

Hardness

6-6.5

Streak

White

Specific Gravity

2.6-2.74 Typical:2.68

Toughness

Fair

Inclusions

The eye in cat's-eye scapolite is distinct and sharp. White, pink or violet material appears fibrous because hollow tubes create the chatoyancy. The cats-eye in reddish brown and brown material is caused by black and orange-red needle like crystals, elongated platelets or dendritic inclusions.

Luster

Vitreous

Stability

Fracture

Conchoidal

Cleavage

Good, in two directions

Comments

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