Star Garnet | Gemopedia

Star garnet exhibits the optical phenomenon called asterism, a star-like pattern created on the surface of a gemstone when light encounters parallel fibrous, or needle-like, inclusions within its crystal structure. Light that strikes the inclusions within the gem reflects off of the inclusions, creating a narrow band of light. When two or more intersecting bands appear, a star pattern is formed. Depending on the crystal, the star may have four, six, or even twelve rays. When only one band forms, it is classified as a "cat's eye".
Alternate
Names
Star Rhodolite
Colors
Light To Dark Purplish Red To Reddish Purple

Star Garnet Classification

Common Name

Star Garnet

Species

Pyrope-Almandite

Variety

Star Garnet

Colors

Light To Dark Purplish Red To Reddish Purple

Alternate Names

Star Rhodolite

Gemstone Groups

Garnet

Key Separations

refractive index, SR nature and spectrum. Color is also helpful. Stones with SG lower than 3.8 and a RI lower than 1.76 are pyrope and those with higher SG are almandine.

Comments

Stone are only star rhodolite if there is a purple component to the color.

Star Garnet Optical Properties

Transparency

Transparent - Translucent

Refractive Index

1.75-1.78

Birefringence

0-0

Optic Character

NA

Optic Sign

NA

Polariscope Reaction

Singly Refractive (SR) With ADR

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

None

Dispersion

Strength: moderate fire Value: 0.026

Comments

Star Garnet Chemistry & Crystallography

Chemical Name

magnesium iron aluminum silicate

Chemical Formula

((Mg,Fe)3Al2(SiO4)3)

Synthesis

Crystal System

Cubic

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline

Comments

Star Garnet Characteristic Physical Properties

Hardness

7-7.5

Streak

White

Specific Gravity

3.74-3.94 Typical:3.84

Toughness

Good

Inclusions

Pyrope-almandite garnet is a type II clarity stone. Needle like inclusions produce 4 to 6 rayed stars and will sometimes show both in well cut stones. Stones might have zircon crystals with stain halos and irregular rounded included crystals that might be zircon or apatite.

Luster

SubAdamantine

Stability

Good

Fracture

Conchoidal

Cleavage

None

Comments

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