Comparison · Minerals
Calcite vs Corundum
Calcite and Corundum are easy to confuse because both are minerals. Corundum is harder (Mohs 9) than Calcite (Mohs 3), so Corundum will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Calcite and Corundum
- Corundum is harder (Mohs 9) than Calcite (Mohs 3), so Corundum will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
- Streak color differs: Calcite leaves a white streak on unglazed porcelain, Corundum leaves white (colorless).
- Corundum feels noticeably heavier for its size (specific gravity 3.95–4.10 versus 2.7 for Calcite).
- Hold a thin edge to the light: Calcite is transparent, Corundum is Transparent to translucent.
- They overlap in clear, yellow, blue, green, and pink, but Calcite also comes in orange and Corundum also comes in red and gray.
- Well-formed crystals give it away: Calcite is trigonal, Corundum is Trigonal.
Calcite vs Corundum properties
| Property | Calcite | Corundum |
|---|---|---|
| Type | Minerals | Minerals |
| Mohs hardness | 3 | 9 |
| Luster | vitreous | Adamantine to vitreous |
| Streak | White | White (colorless) |
| Transparency | transparent | Transparent to translucent |
| Specific gravity | 2.7 | 3.95–4.10 |
| Crystal system | trigonal | Trigonal |
| Common colors | Colorless, White, Yellow, Orange, Blue, Green, Pink | Red (ruby), Blue (sapphire), Colorless, Yellow, Green, Pink, Gray |
| Rarity | common | common |
| Typical specimen value | $2–$100+ | $2–$150+ |
Which is more valuable?
Corundum is usually the more valuable of the two: a typical collector specimen runs about $20 against $15 for Calcite, and premium Corundum can reach $150 or more.
About Calcite
Calcite is one of the most common minerals on Earth, found in sedimentary, metamorphic, and igneous rocks. It's the primary component of limestone and marble.
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.
Calcite vs Corundum FAQ
Is Calcite the same as Corundum?
No. Both are minerals, but they are distinct species with different hardness, streak or luster. Corundum is harder (Mohs 9) than Calcite (Mohs 3), so Corundum will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
How can you tell Calcite from Corundum?
Corundum is harder (Mohs 9) than Calcite (Mohs 3), so Corundum will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Streak color differs: Calcite leaves a white streak on unglazed porcelain, Corundum leaves white (colorless). Corundum feels noticeably heavier for its size (specific gravity 3.95–4.10 versus 2.7 for Calcite).
Which is harder, Calcite or Corundum?
Corundum is harder: Mohs 9 against Mohs 3 for Calcite.
Which is more valuable, Calcite or Corundum?
Corundum is usually the more valuable of the two: a typical collector specimen runs about $20 against $15 for Calcite, and premium Corundum can reach $150 or more.
