Star Ruby | Gemopedia

Star ruby 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".
Colors
Red, Orangy Red To Purplish Red

Star Ruby Classification

Common Name

Star Ruby

Species

Corundum

Variety

Star Ruby

Colors

Red, Orangy Red To Purplish Red

Alternate Names

Gemstone Groups

Key Separations

Appearance, RI and magnification

Comments

Stones are usually cut as cabochons.

Star Ruby Optical Properties

Transparency

Semitransparent - Opaque

Refractive Index

1.762-1.77
Tolerance:(+0.009/-0.005)

Birefringence

0.008-0.01

Optic Character

Uniaxial

Optic Sign

Negative

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Weak to strong red
LWUV: Weak to strong red

CCF Reaction

Pleochroism

Unobservable

Dispersion

Strength: moderate fire Value: 0.018

Comments

Star Ruby Chemistry & Crystallography

Chemical Name

aluminum oxide

Chemical Formula

Al2O3

Synthesis

Crystal System

Trigonal

Classification

Oxide

Nature

Natural

Crystallinity

Crystalline to Aggregate

Comments

Star Ruby Characteristic Physical Properties

Hardness

9

Streak

White

Specific Gravity

4.1-3.95 Typical:4

Toughness

Varies

Inclusions

Star rubies will have silk or sets of parallel rutile needles that produce a 6-rayed star, hexagonal growth lines, color zoning, liquid, negative and mineral inclusions. Some stone might show twinning.

Luster

SubAdamantine

Stability

Very Good

Fracture

Conchoidal

Cleavage

None

Comments

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