Apatite (Cat's-Eye) | Gemopedia

The term cat's eye, or chatoyancy, is used to describe a phenomenal optical property in gemstones, in this case apatite. 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. Chatoyancy is the only known phenomenon seen in apatite. The most common colors for cat's eye apatite are bluish green, green and yellow. Brazil and Sri Lanka are the principal sources of chatoyant apatite, although it may also be found in Madagascar and Tanzania.
Alternate
Names
Fluorapatite
Colors
Bluish Green To Yellowish Green

Apatite (Cat's-Eye) Classification

Common Name

Apatite (Cat's-Eye)

Species

Apatite

Variety

Cat's-Eye Apatite

Colors

Bluish Green To Yellowish Green

Alternate Names

Fluorapatite

Gemstone Groups

Key Separations

RI, spectrum, fluorescence and SG

Comments

Sometimes a distorted optic figure is observed and can be mistaken for a biaxial figure. Most gemstones are Ca5(PO4)3F Calcium Fluroro Phosphate

Apatite (Cat's-Eye) Optical Properties

Transparency

Transparent - Translucent

Refractive Index

1.634-1.638
Tolerance:(+0.012/-0.006)

Birefringence

0.002-0.008

Optic Character

Uniaxial

Optic Sign

Negative

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Variable
LWUV: Variable

CCF Reaction

Pleochroism

Unobservable

Dispersion

Strength: weak fire Value: 0.013

Comments

Apatite (Cat's-Eye) Chemistry & Crystallography

Chemical Name

calcium phosphate with fluorine, chlorine or hydroxyl group

Chemical Formula

Ca5(PO4)3(F,OH,Cl)

Synthesis

Crystal System

Hexagonal

Classification

Phosphate

Nature

Natural

Crystallinity

Crystalline

Comments

Apatite (Cat's-Eye) Characteristic Physical Properties

Hardness

5

Streak

White To Yellow-Gray

Specific Gravity

3.13-3.23 Typical:3.18

Toughness

Fair

Inclusions

Apatite is a type II stone. Fairly well defined chatoyant band that is made up of finer tubular inclusions than cat's-eye tourmaline.

Luster

Vitreous

Stability

Fair

Fracture

Conchoidal, Uneven

Cleavage

Poor, in two directions

Comments

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