---
title: "Topaz: meaning in gemology"
description: "Topaz is a gem mineral with an exceptionally wide color range. Impurity elements or defects in its crystal structure cause its color."
url: https://digitalgemology.com/learn/glossary/topaz
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

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[Glossary](https://digitalgemology.com/learn/glossary) · Colored gemstones

# Topaz

Also called imperial topaz, blue topaz

Topaz is a gem mineral with an exceptionally wide color range. Impurity elements or defects in its crystal structure cause its color.

## Properties

**Gemological properties of topaz**

| Refractive index | 1.619 to 1.627 (GIA); full range 1.606 to 1.644 by F/OH content (LibreTexts, gemdat) |
| --- | --- |
| Birefringence | 0.008 to 0.010 |
| Optic character | Doubly refractive (biaxial) |
| Dispersion | 0.014 |
| Specific gravity | 3.53 (GIA); 3.50 to 3.57 by color (IGS) |
| Hardness (Mohs) | 8 |
| Crystal system | Orthorhombic |
| Pleochroism | Distinct: bright blue, pale rose, colorless |
| Absorption spectrum | Weak line in heat-treated pink stones; otherwise the spectrum is not diagnostic, 682 nm (Cr) |

Published values. They change a little from stone to stone. Our tools do not model topaz yet. Sources: [GIA](https://www.gia.edu/topaz) · [International Gem Society](https://www.gemsociety.org/article/topaz-jewelry-and-gemstone-information/) · [LibreTexts Gemology](https://geo.libretexts.org/Bookshelves/Geology/Gemology/16%3A_Gemstones/16.68%3A_Topaz) · [Gemdat](https://www.gemdat.org/gem-3996.html)

## In more detail

Chromium causes the natural pink, red and violet colors. Blue topaz is hardly ever natural: treatment of colorless topaz gives the blue. A thin metallic oxide coating is another treatment, and abrasive cleaners can remove it. Topaz has cleavage and poor toughness, so protect it from hard blows, heat, steam and ultrasonic cleaners.

## Related terms

- [Aquamarine](https://digitalgemology.com/learn/glossary/aquamarine): Aquamarine is the green-blue to blue variety of the mineral beryl. Emerald and morganite belong to the same species.
- [Cleavage](https://digitalgemology.com/learn/glossary/cleavage): Cleavage is a mineral's tendency to split along flat planes in its crystal structure. A hard knock in a cleavage direction can split a stone.
- [Toughness](https://digitalgemology.com/learn/glossary/toughness): Toughness is a gem's resistance to chipping and breaking. It differs from hardness, which is resistance to scratching.
- [Irradiation](https://digitalgemology.com/learn/glossary/irradiation): Irradiation is exposing a gem to artificial radiation to change its color. Heating sometimes follows, to modify the color further.
- [Coating](https://digitalgemology.com/learn/glossary/coating): Coating is a thin film, paint or ink on the surface of a gem that changes its color or look.
- [Heat treatment](https://digitalgemology.com/learn/glossary/heat-treatment): Heat treatment is controlled heating of a gem to change its color or clarity.

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