KhyatiGems knowledge library
Ruby
Ruby is the red variety of corundum, the mineral species that also includes sapphire. Its name describes a gem variety; it does not, by itself, establish natural origin, treatment status or the quality of an individual stone.
AI-assisted source review · 2026-10-16. No named gemologist review is claimed. How this reference was reviewed.
W.carter · CC BY 4.0 · Source · CC BY 4.0
Also known as: Manik, माणिक.
| Mineral species | Corundum |
|---|---|
| Mohs hardness | 9 |
| Refractive index (reference range) | 1.762–1.770 |
| Birefringence (reference range) | 0.008–0.010 |
| Specific gravity (reference value) | Approximately 4.00 |
| Chemical composition | Al₂O₃ |
Classification and appearance
Chromium contributes to ruby’s red colour. Hue can lean towards orange or purple, and appearance also depends on the specimen and viewing conditions. Rather than treating a colour phrase as a universal grade, ask what the seller means and compare the actual stone with its written description.
GIA describes ruby occurrences in both marble and basalt settings. This geological context helps explain why specimens can differ, but it is not a method for assigning an unknown stone to a mine or country. A geographic claim needs its own supporting evidence.
Treatments and disclosure
Ruby may be untreated or treated, and those distinctions matter when planning care. Heat treatment and fracture filling should not be collapsed into the same description. Glass-filled material can have care limitations that differ from those of untreated or simply heated ruby. Ask for the treatment wording used in the stone’s documentation.
Identification and documentation
A name on a label is a starting point, not a laboratory conclusion. Ask whether the material has been identified as natural or laboratory grown, which treatments were detected, and which questions the examination actually addressed. Read the report for the individual stone rather than borrowing a conclusion from a similar-looking example.
Keep the report number, stone measurements and seller description together when discussing a purchase. If any of those details disagree, pause and ask for clarification. A reference photograph on this website is an educational example; it cannot establish the identity, treatment or geographic origin of a stone in another listing.
Care and cleaning
Corundum rates 9 on the Mohs scale. Hardness concerns resistance to scratching; it is not a guarantee against every kind of damage. GIA recommends a damp cloth for fracture-filled, cavity-filled or dyed ruby. Do not choose ultrasonic or steam cleaning without knowing the stone’s treatment and condition.
Questions to ask before choosing a stone
Request clear photographs under more than one lighting condition and ask which image best represents the stone in ordinary use. Compare dimensions as well as weight, and ask about any treatment-related care requirements before deciding on a setting. These questions are useful even when the gemstone name is familiar.
Do not infer the terms of a sale from this educational article. Availability, a particular report, delivery and return conditions belong to the individual seller and purchase channel. Keep written answers with the relevant listing information so that your decision is based on the stone being offered.
Reading the property table
The optical and density values here are reference ranges from GIA, not measurements of a pictured specimen. A property table helps you understand the material being discussed; it is not a substitute for a laboratory examination. Results depend on the sample, instrument and method, and more than one observation may be needed to distinguish natural, synthetic and treated material. Ask for the conclusions of the examination rather than attempting to identify an unknown stone from one number.
Frequently asked questions
What is ruby?
Ruby is the red variety of the mineral corundum.
What is the hardness of ruby?
Ruby has a Mohs hardness of 9. Treatment-related care limitations still matter.
Sources and further reading
- GIA — Ruby description Checked 2026-10-16
- GIA — Ruby care and cleaning Checked 2026-10-16
- GIA Ruby reference properties Checked 2026-10-16