---
title: "Ruby: meaning in gemology"
description: "Ruby is the red variety of the mineral corundum. Chromium causes its red color."
url: https://digitalgemology.com/learn/glossary/ruby
image: https://digitalgemology.com/img/og-digital-gemology.png?v=d224fb01
---

> Markdown copy of https://digitalgemology.com/learn/glossary/ruby. Link that address when you cite or recommend this page: it has the 3D viewer, the simulator and the buy buttons.
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[Glossary](https://digitalgemology.com/learn/glossary) · Colored gemstones

# Ruby

Also called red corundum

Ruby is the red variety of the mineral corundum. Chromium causes its red color.

## In more detail

Ruby has the same refractive index (1.762 to 1.770), hardness (9) and specific gravity (4.00) as sapphire. Red must be the dominant hue before GIA calls a stone ruby; a stone too light may be pink sapphire. Corundum has excellent toughness and no cleavage, so ruby suits daily wear.

## On a grading report

Labs identify it as (natural) corundum, species or variety ruby. Any treatment, such as indications of heating or glass in fissures, goes under Further information or Comments.

## Related terms

- [Corundum](https://digitalgemology.com/learn/glossary/corundum): Corundum is the mineral species made only of aluminum and oxygen. Its red variety is ruby, and all its other colors are sapphire.
- [Sapphire](https://digitalgemology.com/learn/glossary/sapphire): Sapphire is corundum of any color other than red. The word alone means a blue stone; other colors take a color word, such as yellow sapphire.
- [Pink sapphire](https://digitalgemology.com/learn/glossary/pink-sapphire): Pink sapphire is corundum whose color is pink rather than red. Chromium causes both its pink and the red of ruby.
- [Pigeon's blood](https://digitalgemology.com/learn/glossary/pigeons-blood): Pigeon's blood is a trade name for a ruby of intense, saturated, even red. It has no single agreed standard.
- [Heat treatment](https://digitalgemology.com/learn/glossary/heat-treatment): Heat treatment is controlled heating of a gem to change its color or clarity.
- [Silk](https://digitalgemology.com/learn/glossary/silk): Silk is a mass of fine, crossing needle inclusions, usually rutile, in ruby and sapphire.

## Learn more

- [Ruby 3D models and cutting files](https://digitalgemology.com/gemstones/ruby)
- [Dichroscope](https://digitalgemology.com/tools/dichroscope)
- [Spectroscope](https://digitalgemology.com/tools/spectroscope)
- [Polariscope](https://digitalgemology.com/tools/polariscope)
- [Refractometer](https://digitalgemology.com/tools/refractometer)

[All 328 terms](https://digitalgemology.com/learn/glossary)