Quartz (Cat's-Eye) | Gemopedia

The term cat's eye, or chatoyancy, is used to describe a phenomenal optical property in gemstones, in this case quartz gems. 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.
Colors
Brownish Yellow, Brownish Green, Green-Yellow To Gray

Quartz (Cat's-Eye) Classification

Common Name

Quartz (Cat's-Eye)

Species

Quartz

Variety

Cat's-Eye Quartz

Colors

Brownish Yellow, Brownish Green, Green-Yellow To Gray

Alternate Names

Gemstone Groups

Key Separations

Appearance, RI and SG. Magnification and fluorescence might be helpful. A bull's-eye optic figure is determinative for quartz; may also show Airy's spiral optic figure and Brazil-law twinning under crossed polarizing filters.

Comments

Quartz (Cat's-Eye) Optical Properties

Transparency

Semitransparent - Translucent

Refractive Index

1.544-1.553
Tolerance:very constant

Birefringence

0.009

Optic Character

Uniaxial

Optic Sign

Positive

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

Unobservable

Dispersion

Comments

Quartz (Cat's-Eye) Chemistry & Crystallography

Chemical Name

silicon dioxide (aka silica)

Chemical Formula

SiO2

Synthesis

Crystal System

Trigonal

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline to Aggregate

Comments

Quartz (Cat's-Eye) Characteristic Physical Properties

Hardness

7

Streak

Specific Gravity

2.64-2.69 Typical:2.66

Toughness

Good

Inclusions

Cat's-eye quartz has parallel needle-like inclusions that are typically asbestos or rutile.

Luster

Vitreous

Stability

Good

Fracture

Conchoidal

Cleavage

None

Comments

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