Comparison · Minerals vs Precious Stones
Corundum vs Ruby
Corundum and Ruby are easy to confuse. Both sit near Mohs 9, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Corundum and Ruby
- Both sit near Mohs 9, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Streak color differs: Corundum leaves a white (colorless) streak on unglazed porcelain, Ruby leaves white.
- Hold a thin edge to the light: Corundum is Transparent to translucent, Ruby is transparent.
- They overlap in red and pink, but Corundum also comes in blue, clear, yellow, green, and gray.
- Well-formed crystals give it away: Corundum is Trigonal, Ruby is trigonal.
Corundum vs Ruby properties
| Property | Corundum | Ruby |
|---|---|---|
| Type | Minerals | Precious Stones |
| Mohs hardness | 9 | 9 |
| Luster | Adamantine to vitreous | adamantine |
| Streak | White (colorless) | White |
| Transparency | Transparent to translucent | transparent |
| Specific gravity | 3.95–4.10 | 4 |
| Crystal system | Trigonal | trigonal |
| Common colors | Red (ruby), Blue (sapphire), Colorless, Yellow, Green, Pink, Gray | Red, Pinkish Red, Purplish Red |
| Rarity | common | rare |
| Typical specimen value | $2–$150+ | $1000–$100000+ |
Which is more valuable?
Ruby is usually the more valuable of the two: a typical collector specimen runs about $10000 against $20 for Corundum, and premium Ruby can reach $100000 or more.
About Corundum
Corundum is aluminum oxide, Al2O3, crystallizing in the trigonal system and ranking as the second-hardest natural mineral after diamond. Its gem varieties, red ruby and every other color of sapphire, are colored by trace amounts of chromium, iron, or titanium substituting into an otherwise colorless crystal structure. Non-gem corundum is widely used as an industrial abrasive under the name emery.
About Ruby
Ruby is a red variety of corundum, the second hardest natural mineral. Its intense red color comes from chromium impurities.
Corundum vs Ruby FAQ
Is Corundum the same as Ruby?
No. Corundum is a mineral while Ruby is a precious stone. Both sit near Mohs 9, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Corundum from Ruby?
Both sit near Mohs 9, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Streak color differs: Corundum leaves a white (colorless) streak on unglazed porcelain, Ruby leaves white. Hold a thin edge to the light: Corundum is Transparent to translucent, Ruby is transparent.
Which is harder, Corundum or Ruby?
They are about equally hard, both near Mohs 9.
Which is more valuable, Corundum or Ruby?
Ruby is usually the more valuable of the two: a typical collector specimen runs about $10000 against $20 for Corundum, and premium Ruby can reach $100000 or more.
