Comparison · Minerals
Calcite vs Forsterite
Calcite and Forsterite are easy to confuse because both are minerals. Forsterite is harder (Mohs 6.5–7) than Calcite (Mohs 3), so Forsterite 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 Forsterite
- Forsterite is harder (Mohs 6.5–7) than Calcite (Mohs 3), so Forsterite will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not.
- Forsterite feels noticeably heavier for its size (specific gravity 3.2–3.3 versus 2.7 for Calcite).
- Hold a thin edge to the light: Calcite is transparent, Forsterite is Transparent to translucent.
- They overlap in clear, yellow, and green, but Calcite also comes in orange, blue, and pink.
- Well-formed crystals give it away: Calcite is trigonal, Forsterite is Orthorhombic.
Calcite vs Forsterite properties
| Property | Calcite | Forsterite |
|---|---|---|
| Type | Minerals | Minerals |
| Mohs hardness | 3 | 6.5–7 |
| Luster | vitreous | Vitreous |
| Streak | White | White |
| Transparency | transparent | Transparent to translucent |
| Specific gravity | 2.7 | 3.2–3.3 |
| Crystal system | trigonal | Orthorhombic |
| Common colors | Colorless, White, Yellow, Orange, Blue, Green, Pink | Pale yellow-green, Olive green, Colorless |
| Rarity | common | common |
| Typical specimen value | $2–$100+ | $2–$150+ |
Which is more valuable?
Forsterite is usually the more valuable of the two: a typical collector specimen runs about $20 against $15 for Calcite, and premium Forsterite 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 Forsterite
Forsterite is the magnesium-rich end member of the olivine mineral series, with the formula Mg2SiO4, and its gem-quality transparent green variety is known as peridot. It crystallizes directly from magnesium-rich magma and is one of the first minerals to form as basaltic and ultramafic melts cool. Forsterite is abundant in Earth's upper mantle, where the olivine-rich rock peridotite is believed to make up much of that layer.
Calcite vs Forsterite FAQ
Is Calcite the same as Forsterite?
No. Both are minerals, but they are distinct species with different hardness, streak or luster. Forsterite is harder (Mohs 6.5–7) than Calcite (Mohs 3), so Forsterite 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 Forsterite?
Forsterite is harder (Mohs 6.5–7) than Calcite (Mohs 3), so Forsterite will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Forsterite feels noticeably heavier for its size (specific gravity 3.2–3.3 versus 2.7 for Calcite). Hold a thin edge to the light: Calcite is transparent, Forsterite is Transparent to translucent.
Which is harder, Calcite or Forsterite?
Forsterite is harder: Mohs 6.5–7 against Mohs 3 for Calcite.
Which is more valuable, Calcite or Forsterite?
Forsterite is usually the more valuable of the two: a typical collector specimen runs about $20 against $15 for Calcite, and premium Forsterite can reach $150 or more.
