---
title: "Glass: meaning in gemology"
description: "Glass is a man-made material and one of the oldest gem imitations still in use. It can be made in almost any color."
url: https://digitalgemology.com/learn/glossary/glass
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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

# Glass

Also called paste, glass imitation

Glass is a man-made material and one of the oldest gem imitations still in use. It can be made in almost any color.

## Properties

**Gemological properties of glass**

| Refractive index | 1.470 to 1.700 (crown glass about 1.5 to 1.6; lead glass higher) |
| --- | --- |
| Birefringence | None (singly refractive) |
| Optic character | Singly refractive (amorphous) |
| Dispersion | Not given by our sources |
| Specific gravity | 2.30 to 4.50 (lead raises SG) |
| Hardness (Mohs) | 5 to 6 |
| Crystal system | Amorphous |
| Pleochroism | None |
| Absorption spectrum | Not diagnostic |

Published values. They change a little from stone to stone. Our tools do not model glass yet. Sources: [International Gem Society](https://www.gemsociety.org/article/glass) · [hyperphysics.gsu.edu](https://hyperphysics.gsu.edu/hbase/geoopt/glass.html)

## In more detail

Glass is less brilliant than the gems it imitates, such as amethyst, aquamarine and peridot. It can also copy phenomenal gems like opal and tiger's eye. Glass is also one of the classic diamond simulants, sometimes called paste. Gas bubbles in glass can look like natural inclusions to an untrained eye.

## 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.
- [Assembled stone](https://digitalgemology.com/learn/glossary/assembled-stone): An assembled stone is made of two or more pieces joined together, usually with glue or by fusing. A doublet has two parts; a triplet has three, or two parts with a colored layer between them.
- [Lead-glass filling](https://digitalgemology.com/learn/glossary/lead-glass-filling): Lead-glass filling is a treatment that fills fissures and cavities in corundum, mostly ruby, with high-lead glass to hide them.
- [Fracture filling](https://digitalgemology.com/learn/glossary/fracture-filling): Fracture filling is a clarity treatment that injects a glass-like filler into a crack to make it less visible.
- [Inclusion](https://digitalgemology.com/learn/glossary/inclusion): An inclusion is a clarity characteristic inside a diamond, or one that reaches the surface from inside.

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