What it is confused with
Red spinel, garnet, synthetic ruby and lead-glass-filled ruby. Glass-filled stones are composites worth a fraction of natural ruby and need specialist care.
Red to purplish red
Ruby birthstone
Ruby, the birthstone for July, is aluminum oxide (Al₂O₃) — corundum colored by chromium, red to purplish red, rated 9 on the Mohs scale. Traditionally, it is associated with courage, appetite for life and decisive action — attributed, not demonstrated.
- Mohs hardness
- 9 scratches window glass
- Crystal system
- Trigonal Al₂O₃
- Main sources today
- Myanmar also Mozambique, Thailand
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Properties
Composition
Aluminum oxide (Al₂O₃) — corundum colored by chromium
Hardness (Mohs)
9
Crystal system
Trigonal
Color
Red to purplish red
Mined in
Myanmar, Mozambique, Thailand, Madagascar, Sri Lanka
Worth knowing
Ruby and sapphire are the same mineral. Red corundum is ruby; every other color is sapphire.
History
Traded along the Silk Road from Burma; Sanskrit called it ratnaraj, "king of gems".
Buying
Buying Ruby: fakes, value and treatments
What decides the price
Strong pure red — "pigeon's blood" — is valued most, historically from Mogok in Myanmar. Heat treatment is common and accepted; heavy glass filling is not.
Where it is used
Synthetic ruby made the first working laser in 1960 and still serves as the bearings, or "jewels", in mechanical watches.
A less familiar fact
Synthetic ruby was first produced commercially by Auguste Verneuil's flame-fusion method in the early 1900s.
Practical
Caring for Ruby
How to clean it
Warm soapy water. Safe in ultrasonic unless fracture-filled — and lead-glass-filled rubies are common, so ask.
How to tell it is real
Almost all commercial ruby is heat-treated, which is normal and disclosed. Synthetic ruby has been made since 1902 and is chemically identical; curved growth lines under magnification give it away.
How hard is Ruby?
At 9, ruby is surpassed only by diamond among the stones here. The question to ask is about filling: lead-glass-filled rubies are common, and the glass is far softer and more fragile than the corundum around it. Only Sapphire shares its place on our scale. Among the stones in this reference, the next softer is Alexandrite (8.5) and the next harder Diamond (10).
Ruby, at 9, is harder than 40 of the other 42 stones here and softer than 1.
Traditional associations
Ruby is traditionally associated with courage, appetite for life and decisive action. Chakra in crystal practice: Root, Heart. Element: Fire.
Questions about Ruby
What is Ruby made of?
Aluminum oxide (Al₂O₃) — corundum colored by chromium, crystallizing in the trigonal system.
Which month is Ruby the birthstone for?
July.
Where does Ruby come from?
Myanmar, Mozambique, Thailand, Madagascar, Sri Lanka.
Can Ruby be worn every day?
Yes. It rates 9 on the Mohs scale, and the main thing to watch is glass filling — ask whether the stone is treated.
Cite this page
AstroHot. “Ruby Birthstone: The July Stone — Meaning and Properties.” Accessed October 28, 2026. https://astrohot.com/crystals/gemstones/ruby/
For Wikipedia
{{cite web |title=Ruby Birthstone: The July Stone — Meaning and Properties |url=https://astrohot.com/crystals/gemstones/ruby/ |website=AstroHot |access-date=2026-10-28}}