---
title: "GGG: meaning in gemology"
description: "GGG (gadolinium gallium garnet) is a man-made crystal used as an imitation of diamond. It is a close relative of YAG."
url: https://digitalgemology.com/learn/glossary/ggg
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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[Glossary](https://digitalgemology.com/learn/glossary) · Diamond and simulants

# GGG

Also called gadolinium gallium garnet

GGG (gadolinium gallium garnet) is a man-made crystal used as an imitation of diamond. It is a close relative of YAG.

## Properties

**Gemological properties of GGG**

| Refractive index | 1.970 |
| --- | --- |
| Birefringence | None (singly refractive) |
| Optic character | Singly refractive |
| Dispersion | 0.045 |
| Specific gravity | 7.05 |
| Hardness (Mohs) | 6.5 (6 1/2) |
| Crystal system | Cubic |
| Pleochroism | None |
| Absorption spectrum | Not recorded |

Published values. They change a little from stone to stone. Our tools do not model GGG yet. Sources: [GIA](https://www.gia.edu/dam/migrated-assets/docs/doc1/Winter-1997-Gems-Gemology-Synthetic-Moissanite-Diamond-Substitute.pdf) · [International Gem Society](https://gemsociety.org/article/gadolinium-gallium-garnet-facet-faceting-information) · [Gemdat](https://www.gemdat.org/gem-42919.html)

## In more detail

GGG has about the same fire as diamond. It is much heavier than diamond, so a GGG looks smaller than a diamond of the same carat weight. It is soft, so it scratches fairly easily and often has rounded facet junctions.

## Related terms

- [Simulant](https://digitalgemology.com/learn/glossary/simulant): A simulant is a material that looks like a gem but has a different chemistry, structure and properties. Cubic zirconia, moissanite and glass are diamond simulants.
- [YAG](https://digitalgemology.com/learn/glossary/yag): YAG (yttrium aluminum garnet) is a man-made crystal used as an imitation of diamond. It is made in many colors, and the colorless crystal is cut as a diamond simulant.
- [Cubic zirconia](https://digitalgemology.com/learn/glossary/cubic-zirconia): Cubic zirconia (CZ) is a man-made diamond simulant. GIA names it as the most common simulant today.
- [Diamond](https://digitalgemology.com/learn/glossary/diamond): Diamond is a single element, carbon, with every atom bonded to four neighbors in a cubic crystal. It is the hardest gem, Mohs 10.
- [Specific gravity](https://digitalgemology.com/learn/glossary/specific-gravity): Specific gravity compares a stone's weight with the weight of the same volume of water. It decides how much a stone of a given size weighs.
- [Carat weight](https://digitalgemology.com/learn/glossary/carat-weight): Carat weight is the weight of a gemstone. One carat is 200 milligrams, a fifth of a gram, and it has 100 points.

[All 369 terms](https://digitalgemology.com/learn/glossary)