KEY NUMBERS · SPINEL VS. RUBY
8 vs. 9
Mohs hardness, spinel vs. ruby
30–60%
cheaper, similar quality (trade estimate)
~1/10
top spinel vs. top ruby price (dealer view)
Spinel and ruby are different minerals that can look almost identical. Ruby is red corundum; spinel is magnesium aluminum oxide. They often form in the same marble deposits, which is why red spinel was sold as ruby for centuries.
Today, fine red spinel costs a fraction of comparable ruby: dealers commonly cite 30 to 60% less for similar quality, and about a tenth of the price at the very top.
TL;DR
Ruby: corundum, Al₂O₃, Mohs 9, doubly refractive, pleochroic. Spinel: MgAl₂O₄, Mohs 8, singly refractive, no pleochroism.
Both get their red from chromium, and both fluoresce. Your eye alone cannot separate them reliably.
Some of history's most famous "rubies," including the Black Prince's Ruby in the British Crown, are spinel.
Spinel is rarely treated. Most rubies are heated. That is spinel's strongest argument.
Fine red spinel trades well below fine ruby, but the gap has narrowed as collectors discovered it.
Ruby is corundum. Spinel is its own mineral species, with magnesium in its formula and a cubic crystal system.
Both form in marble rich in aluminum and chromium. In Mogok (Myanmar), Luc Yen (Vietnam) and the Pamirs (Tajikistan), miners recover both from the same gravels.
Before modern gemology, a red stone was a ruby. That is how the roughly 170-carat Black Prince's Ruby in the British Imperial State Crown, and the Timur Ruby, got their names. Both are red spinels.
Red spinel (left) and ruby (right). Face-up, the two can be hard to tell apart. Photos: Smithsonian Institution, National Museum of Natural History (CC0).
How to Tell Spinel From Ruby
Property | Ruby | Spinel |
|---|---|---|
Mineral | Corundum, Al₂O₃ | Spinel, MgAl₂O₄ |
Crystal system | Trigonal (hexagonal barrels, tablets) | Cubic (octahedra) |
Hardness (Mohs) | 9 | 8 |
Refractive index | About 1.762 to 1.770 | About 1.718 |
Optic character | Doubly refractive | Singly refractive |
Pleochroism | Yes: purplish red and orangy red from different angles | None |
Specific gravity | About 4.00 | About 3.60 |
Typical inclusions | Rutile silk, fingerprints, color zoning | Tiny octahedral crystals, often in rows |
Common treatment | Heating, often with residues; glass filling at the low end | Rarely treated |
The tests a gemologist uses
Refractometer. The fastest separation. One reading near 1.718 means spinel; two readings around 1.76 to 1.77 mean ruby.
Polariscope. Spinel stays dark as it rotates (singly refractive). Ruby blinks light and dark.
Dichroscope. Ruby shows two shades of red. Spinel shows one.
Microscope. Rows of tiny octahedral crystals point to spinel; silk and angular zoning point to corundum.
None of this is reliable at home. A UV torch makes both glow red, and both can look identical face-up. If the label matters to the price, the lab decides.
Spinel vs. Ruby Price
Spinel has always traded below ruby, mostly for market reasons, not beauty. Ruby has a larger collector base, standardized grading, centuries of auction history and demand from major jewelry houses.
Reference point | What it says |
|---|---|
Dealer quoted by Rapaport | The finest red spinels have traditionally been about a tenth of the price of the finest rubies |
Trade guides | For similar color and quality, spinel typically prices 30 to 60% below ruby |
US jeweler example | A ruby that might reach $40,000 per carat vs. $1,000 to $7,000 per carat for a spinel of the same size |
GIA | Rising demand has, to a degree, closed the spinel vs. ruby and sapphire price gap |
Our take: think in tiers. At commercial quality the gap barely matters. At the fine tier, spinel is the better value: an untreated vivid spinel often costs less than a heated ruby of lesser color. At the very top the gap is still large, and that is where it is narrowing fastest.
Spinel is one of the stones we track every week.
Auction results, origin trends, and the price signals behind the "undervalued gem" headlines. Every Tuesday.
Which Is Better: Spinel or Ruby?
Choose ruby if
You want maximum hardness for a daily-wear ring (Mohs 9 vs. 8).
You value deep market liquidity and a long auction history.
Your budget allows for a heated stone with good color, or an unheated stone with a top-lab report.
Choose spinel if
You want untreated material without paying unheated-ruby prices.
You prefer vivid, bright reds and pinks; the neon red-pink Mogok material is sometimes sold under the trade name "Jedi."
You want colors ruby cannot offer: cobalt blue, lavender, gray, and the orangy pinks of Mahenge, Tanzania.
Mohs 8 is still very durable. Spinel is perfectly suited to rings, with a little more care than ruby.
Look-Alikes and Fakes
Synthetic spinel has been produced since the early 20th century and was long used to imitate other gems, including aquamarine and blue sapphire. It is cheap; a lab can identify it.
Heated spinel. Uncommon, but it exists. Heating can lower value in collectors' eyes; ask for a report on any significant stone.
Garnet and glass are the usual low-end impostors for both stones. See Ruby vs. Garnet.
For the deeper story on spinel, read What Is Spinel?
FAQ
Is spinel a type of ruby? No. Spinel is a separate mineral species. Red spinel was historically called ruby, but the two are chemically and structurally different.
Is spinel cheaper than ruby? Yes, for comparable color and quality. Trade estimates put spinel roughly 30 to 60% below ruby, and about a tenth of the price at the very top.
Can you tell spinel from ruby with the naked eye? Not reliably. A refractometer, polariscope or dichroscope separates them quickly; a lab report settles it.
Is spinel heat treated? Rarely. Most spinel on the market is untreated, which is a major part of its appeal.
Is spinel a good stone for an engagement ring? Yes. At Mohs 8 with no cleavage, spinel is durable enough for daily wear.
Why is spinel so cheap? It isn't cheap at the top, but its market is smaller, less standardized, and younger than ruby's. As demand grows, prices for fine material have risen.
Spinel and ruby are two of eight stones we track weekly.
The Carat Index, live auction alerts, and the full archive, every Tuesday.
Useful Sources
GIA, Spinel Quality Factors: color, clarity and the narrowing price gap.
Rapaport, Spinel Steps Into the Spotlight: dealer views on spinel vs. ruby pricing.
Shreve, Spinel: An Imposter No Longer: retail price comparison.
Lotus Gemology, Auction Records: ruby, sapphire and spinel results.