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.
| 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 |
| 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 |
| Chemical Formula | Gd3Ga5O12 |
| Crystal System | Cubic |
Colorless 
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.
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.
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.
Showcasing 200 gemstones in over 1,000 pages and accompanied by more than 2,000 photos, The Sisk Gemology Reference is a must-have in every collector’s library. Each comprehensive, three-volume set features state-of-the-art photography, detailed illustrations, and scientifically precise descriptions to create an entrancing experience for gemstone amateurs and afficionados alike.
This page was created on June 27, 2014.
This page was last edited on October 24, 2019.
