Corundum With Star Induced By Lattice Diffusion | 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.

Corundum With Star Induced By Lattice Diffusion Classification

Common Name

Corundum With Star Induced By Lattice Diffusion

Species

Corundum

Variety

Corundum With Star Induced By Lattice Diffusion

Colors

blue

Alternate Names

Gemstone Groups

Key Separations

magnification and appearance

Comments

Corundum With Star Induced By Lattice Diffusion Optical Properties

Transparency

Semitransparent To 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) or AGG depending on transparency

Fluorescence

SWUV: light blue stones weak or moderate to strong red, dark stones inert
LWUV: light blue stones weak or moderate to strong red, dark stones inert

CCF Reaction

Pleochroism

Value: usually none to weak same as non asterism stones and it depends on transparency

Dispersion

Strength: weak fire Value: 0.018

Corundum With Star Induced By Lattice Diffusion Chemistry & Crystallography

Chemical Name

aluminum oxide

Chemical Formula

Al2O3

Synthesis

Crystal System

Trigonal

Classification

Oxide

Nature

Natural

Crystallinity

Crystalline

Corundum With Star Induced By Lattice Diffusion Characteristic Physical Properties

Hardness

9

Streak

white

Specific Gravity

4.1-3.95 Typical: 4

Toughness

Good To Excellent

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 To Vitreous

Stability

Very Good

Fracture

Conchoidal

Cleavage

None, May Show Parting On Twinned Stones

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