Gadolinium Gallium Garnet (GGG, Gd3Ga5O12) is a synthetic crystalline material of the garnet group, with good mechanical, thermal, and optical properties. It is typically colorless. It has cubic lattice, density 7.08 g/cm3 and Mohs hardness is variously noted as 6.5 and 7.5. Its crystals are made by Czochralski method and can be made with addition of various dopants for modification of color. It is used in fabrication of various optical components and as substrate material for magneto–optical films. It also finds use in jewelry as a diamond simulant.

Chemical Composition: 

Gadolinium Gallium Oxide - Gd₃Ga₅O₁₂

Classification / Type: 

GGG is a man made material with a garnet internal structure. The term synthetic is not used to refer to this material, since it does not have a natural counterpart.

Colors / Varieties: 

Colorless, red, blue, green.

Crystal System / Forms: 

Cubic System

Hardness: 

5.5 - 6.5

Specific Gravity: 

7.02 - 7.09

Cleavage / Fracture: 

Nil / Conchoidal fracture.

Optic Character: 

Isotropic (S.R.)

Lustre: 

Adamantine to vitreous

Refractive Index / Birefringence: 

1.970; Range: 1.920 - 2.030

Pleochroism: 

None

Dispersion: 

0.045

Magnification: 

Generally clean

U.V. Fluorescence: 

• Colorless Impregnation: Strong yellow in longwave and weak yellow in shortwave.
• Colored Impregnation (Dyeing): Varies with dopants used.

Spectrum: 

Not characteristic

Cause of Color: 

Varies with dopants used.

Specific Tests: 

Moderate see through effect.

Synthesis: 

Czochralski Method

Simulants (with separation tests): 

Y.A.G. (S.G.), Synthetic Cubic Zirconia (S.G., dispersion), Diamond (S.G., inclusions), Strontium Titanate (S.G., dispersion), Sphene (optic character, doubling, dispersion), Synthetic Rutile (optic character, dispersion, doubling), Demantoid (spectrum, inclusions, S.G.), Spessartite (spectrum, inclusions, S.G.), Malaya Garnet (spectrum, inclusions, S.G.)

Sources: 

In a laboratory. No natural counterpart.

Cuts & Uses: 

Facetted cuts, beads, etc.