Gadolinium Gallium Garnet (GGG)

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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.

Gadolinium Gallium Garnet (GGG) Polished
GGG Classification
Common Name GGG
GGG Optical Properties
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
GGG Characteristic Physical Properties
Hardness 6.5
Specific Gravity 6.950-7.090 Typical:7.05
Inclusions Generally inclusion free but might have gas bubbles.
Luster Vitreous, SubAdamantine
Fracture Conchoidal
Cleavage None
GGG Chemistry & Crystallography
Chemical Formula Gd3Ga5O12
Crystal System Cubic

Gadolinium Gallium Garnet (GGG) Colors

  • Colorless Gadolinium Gallium Garnet (GGG) Colorless

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.

Jewelry Television acknowledges 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.

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Tim Matthews

Author

Tim Matthews

Tim Matthews is President and Chief Executive Officer of Jewelry Television® (JTV), as well as a member of the company's Board of Directors. He oversees and leads all aspects of the company's powerful omni-digital retail platform that uniquely specializes in fine jewelry and gemstones. His passion for business and gemstones has led him to become a recognized expert in the field of gemology. He is a life member of the Gemmological Association of Great Britain (Gem-A) and has earned Gem-A's highest degrees, the Gemmology (FGA) and Diamond (DGA) diplomas. He is also a Graduate Gemologist (GG) of the Gemological Institute of America (GIA) and has also completed GIA's Graduate Diplomas in Diamonds, Colored Stones and Pearls. Under his leadership, JTV has become the leader in the sourcing and selling of color gemstones and jewelry.

This page was created on June 27, 2014.

This page was last edited on October 24, 2019.