Star Almandite Garnet | Gemopedia

Star almandite 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 Garnet
Colors
Brownish Orange To Brownish Red, Reddish Orange To Red, Slightly Purplish Red To Reddish Purple

Star Almandite Garnet Classification

Common Name

Star Almandite Garnet

Species

Almandite Garnet

Variety

Star Almandite Garnet

Colors

Brownish Orange To Brownish Red, Reddish Orange To Red, Slightly Purplish Red To Reddish Purple

Alternate Names

Star Garnet

Gemstone Groups

Garnet

Key Separations

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

Comments

Star Almandite Garnet Optical Properties

Transparency

Semitransparent - Semitranslucent

Refractive Index

Over The Limit 1.78-1.82
Tolerance:(+0.030/-0.030)

Birefringence

Optic Character

NA

Optic Sign

NA

Polariscope Reaction

Singly Refractive (SR) With ADR

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

None

Dispersion

Strength: weak fire Value: 0.024

Comments

Star Almandite Garnet Chemistry & Crystallography

Chemical Name

iron aluminum silicate

Chemical Formula

Fe3Al2(SO4)3

Synthesis

Crystal System

Cubic

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline

Comments

Star Almandite Garnet Characteristic Physical Properties

Hardness

7-7.5

Streak

Specific Gravity

3.93-4.3 Typical:4.05

Toughness

Good

Inclusions

Almandite garnet is a type II clarity stone. Displays 4 or 6 rayed stars and sometimes well cut stones will show both. Stones are often found with needles that intersect at 70o to 110o angles. Zircon crystals are commonly seen with strain halos. Irregular or rounded crystals can also be found.

Luster

SubAdamantine

Stability

Good

Fracture

Conchoidal

Cleavage

None

Comments

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