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Gadolinium Gallium Garnet (GGG)

By Tim Matthews, JD, FGA, GG, DGA,
CEO and President of JTV (retired)
Published: June 2014
Modified: September 2023
Gadolinium Gallium Garnet (GGG) Polished
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Table of Contents
  • General Information
  • Gadolinium Gallium Garnet (GGG) Colors
  • Gadolinium Gallium Garnet (GGG) Spectra
  • Countries of Origin
  • Care

Gadolinium gallium garnet, thankfully abbreviated to GGG, is a man-made diamond simulant that entered the market in the 1960's. Today it is rarely used as a gemstone, and is instead manufactured for optical and industrial uses. The Czochralski method of gem synthesis involves the melting of various elements in a platinum crucible. A small gem crystal (called a seed) and attached to a rod is then dipped into the melt and slowly pulled away as the crystal grows around the seed. For this reason, the Czochralski method is also known as crystal pulling. Synthetic gems have the same chemical, optical, and physical properties of their natural counterparts, but are a more cost-effective alternative to a natural gem.

General Information

  • Classification
  • Optical Properties
  • Characteristic Physical Properties
  • Chemistry & Crystallography
Common Name
GGG
Transparency
Transparent
Dispersion
Strength: Moderate Fire Value: 0.04500
Refractive Index
Over the Limit 1.97-2.03
Optic Character
NA
Optic Sign
NA
Polariscope Reaction
Singly Refractive (SR)
Fluorescence
SWUV: Moderate to strong pinkish orange
LWUV: Inert to moderate orange
Pleochroism
None
Hardness
6.5-7
Streak
White
Specific Gravity
6.950-7.090 Typical:7.05
Toughness
Poor
Inclusions
Generally inclusion free but might have gas bubbles.
Luster
Vitreous, SubAdamantine
Fracture
Conchoidal
Cleavage
None
Chemical Name
Gadolinium Gallium Garnet
Chemical Formula
Gd3Ga5O12
Crystal System
Cubic

Gadolinium Gallium Garnet (GGG) Colors

  • Blue Gadolinium Gallium Garnet (GGG)
    Blue
  • Brown Gadolinium Gallium Garnet (GGG)
    Brown
  • Colorless Gadolinium Gallium Garnet (GGG)
    Colorless
  • Green Gadolinium Gallium Garnet (GGG)
    Green
  • Pink Gadolinium Gallium Garnet (GGG)
    Pink
  • Purple Gadolinium Gallium Garnet (GGG)
    Purple
  • Red Gadolinium Gallium Garnet (GGG)
    Red
  • Yellow Gadolinium Gallium Garnet (GGG)
    Yellow

Gadolinium Gallium Garnet (GGG) Spectra

Gadolinium Gallium Garnet (GGG) Spectra
GADOLINIUM GALLIUM GARNET

Color due to rare earths. This lab created product can have the appearance of a very fine demantoid garnet but a quick look at its spectrum confirms it to be heavily doped with rare earth elements such as neodymium which here is so intense that the groups of lines normally seen have merged to form solid blocks of absorption.

Gadolinium Gallium Garnet (GGG) Spectra
GADOLINIUM GALLIUM GARNET

Color due to rare earths. Gadolinium Gallium Garnet provides a blue gemstone similar in appearance to a fine sapphire or a cobalt spinel. However, the typical multi-band spectrum due to neodymium suggests otherwise. As the lines in the green, yellow and red areas may merge as dark broad areas of absorption, not unlike a cobalt spectrum, an intense light source is required to resolve the individual lines in these areas.

Gadolinium Gallium Garnet (GGG) Spectra
GADOLINIUM GALLIUM GARNET

Broad absorption is centered in the green at 525nm. stretching over approximately 120nm. Red and orange are freely transmitted with a small window of deep blue-violet before total absorption from 445nm. This broad center band comprises four strong absorption peaks at approximately 532nm; 527nm; 515nm; and 504nm. which merge to form this dark area.

We acknowledge the significant scientific contributions of John S Harris, FGA to the study of gemstone spectra and with deep appreciation to him, acknowledges the use of his images and related notes about gemstones and their spectra in the educational materials on this website.

Countries of Origin

Unknown

Care

Normal care, the toughness is fair to poor so care must be taken to avoid abrasions.

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