What is a ruby gemstone?
By Jared James · Last updated 21 May 2026
Definition
Ruby is a variety of corundum, the mineral form of aluminium oxide, coloured red by traces of chromium in the crystal structure. It ranges from vivid scarlet to deep blood red and into pinkish-red, and along with emerald, diamond and sapphire it is considered one of the four precious gemstones. Ruby is the birthstone for July and second only to diamond in hardness, scoring 9 on the Mohs scale, which makes it excellent for rings and everyday wear. The finest rubies come from Myanmar, Mozambique and Sri Lanka.
Frequently asked questions
- What makes a ruby valuable?
- Colour is the most important factor. The most prized rubies have a vivid, pure red sometimes called pigeon's blood, with no brownish or purplish cast and a strong saturation. Size, clarity and origin also matter; Burmese rubies with no heat treatment command the highest prices at auction.
- How can you tell if a ruby is real?
- A real ruby will scratch glass easily because it is very hard, and it will stay the same colour in different lights rather than shifting dramatically. Many natural rubies are heat-treated to improve colour and clarity, which is standard and disclosed practice; if a ruby is suspiciously perfect or very cheap, synthetic or glass-filled stones are worth checking for.
- What is the difference between ruby and garnet?
- They are different minerals entirely. Ruby is corundum and sits at hardness 9, while red garnets are a different mineral family sitting around 6.5 to 7.5. Garnets tend toward a deeper, more burgundy or orangey red and lack the bright fluorescent quality of a fine ruby under UV light.
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