Comparison · Minerals
Forsterite vs Olivine
Forsterite and Olivine are easy to confuse because both are minerals. Both sit near Mohs 6.5–7, 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 Forsterite and Olivine
- Both sit near Mohs 6.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Olivine feels noticeably heavier for its size (specific gravity 3.3–4.3 versus 3.2–3.3 for Forsterite).
- They overlap in green and yellow, but Forsterite also comes in clear and Olivine also comes in brown.
Forsterite vs Olivine properties
| Property | Forsterite | Olivine |
|---|---|---|
| Type | Minerals | Minerals |
| Mohs hardness | 6.5–7 | 6.5–7 |
| Luster | Vitreous | Vitreous |
| Streak | White | White |
| Transparency | Transparent to translucent | Transparent to translucent |
| Specific gravity | 3.2–3.3 | 3.3–4.3 |
| Crystal system | Orthorhombic | Orthorhombic |
| Common colors | Pale yellow-green, Olive green, Colorless | Olive green, Yellowish green, Brown |
| Rarity | common | common |
| Typical specimen value | $2–$150+ | $2–$150+ |
Which is more valuable?
Typical specimens of Forsterite and Olivine trade in a similar range, around $20.
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.
About Olivine
Olivine is a magnesium iron silicate, (Mg,Fe)2SiO4, forming a solid-solution series between the magnesium-rich end member forsterite and the iron-rich end member fayalite. It crystallizes in the orthorhombic system and is one of the most abundant minerals in Earth's upper mantle. Its gem-quality green variety, peridot, is one of the few gemstones formed deep within the mantle rather than the crust.
Forsterite vs Olivine FAQ
Is Forsterite the same as Olivine?
No. Both are minerals, but they are distinct species with different hardness, streak or luster. Both sit near Mohs 6.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Forsterite from Olivine?
Both sit near Mohs 6.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Olivine feels noticeably heavier for its size (specific gravity 3.3–4.3 versus 3.2–3.3 for Forsterite). They overlap in green and yellow, but Forsterite also comes in clear and Olivine also comes in brown.
Which is harder, Forsterite or Olivine?
They are about equally hard, both near Mohs 6.5–7.
Which is more valuable, Forsterite or Olivine?
Typical specimens of Forsterite and Olivine trade in a similar range, around $20.
