Star Corundum (Lattice-Diffused) | Gemopedia

Corundum with star induced by lattice diffusion has been treated with a heat treatment at high temperatures with beryllium that deeply penetrates the gem material to alter the color. This gem 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 narrow bands of light.
Alternate
Names
Corundum With Star Induced By Lattice Diffusion
Colors
Blue

Star Corundum (Lattice-Diffused) Classification

Common Name

Star Corundum (Lattice-Diffused)

Species

Corundum

Variety

Lattice Diffused Star Corundum

Colors

Blue

Alternate Names

Corundum With Star Induced By Lattice Diffusion

Gemstone Groups

Key Separations

magnification and appearance

Comments

Star Corundum (Lattice-Diffused) 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: Inert to strong red
LWUV: weak to strong red

CCF Reaction

Pleochroism

Unobservable

Dispersion

Strength: weak fire Value: 0.018

Comments

Star Corundum (Lattice-Diffused) Chemistry & Crystallography

Chemical Name

aluminum oxide

Chemical Formula

Al2O3

Synthesis

Crystal System

Trigonal

Classification

Oxide

Nature

Natural

Crystallinity

Crystalline

Comments

Star Corundum (Lattice-Diffused) Characteristic Physical Properties

Hardness

9

Streak

White

Specific Gravity

4.1-3.95 Typical:4

Toughness

Varies

Inclusions

Stars that are induced by lattice diffusion will have a unnaturally sharp or well defined star. The color of the stone is confined to the surface and concentrated around the girdle edge. The stone can have color concentrations in the pits and fractures. None of the rays of the star are perpendicular to the stone's hexagonal growth structure.

Luster

SubAdamantine

Stability

Very Good

Fracture

Conchoidal

Cleavage

None

Comments

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