Comparison · Igneous Rocks vs Quartz Family
Peridotite vs Quartz
Peridotite and Quartz are easy to confuse. Both sit near Mohs 5.5–7, 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 Peridotite and Quartz
- Both sit near Mohs 5.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Peridotite feels noticeably heavier for its size (specific gravity 3.1–3.4 versus 2.65 for Quartz).
- Hold a thin edge to the light: Peridotite is Opaque, Quartz is Transparent to translucent.
- They overlap in yellow and black, but Peridotite also comes in green and Quartz also comes in clear, purple, pink, gray, and brown.
Peridotite vs Quartz properties
| Property | Peridotite | Quartz |
|---|---|---|
| Type | Igneous Rocks | Quartz Family |
| Mohs hardness | 5.5–7 | 7 |
| Luster | Vitreous (olivine and pyroxene grains) | Vitreous, greasy on fracture surfaces |
| Streak | — | White |
| Transparency | Opaque | Transparent to translucent |
| Specific gravity | 3.1–3.4 | 2.65 |
| Crystal system | — | Trigonal |
| Common colors | Green, Dark green, Yellowish green, Black | Colorless, White, Purple (amethyst), Yellow (citrine), Pink (rose), Brown/black (smoky) |
| Rarity | common | common |
| Typical specimen value | $1–$75+ | $5–$250+ |
Which is more valuable?
Quartz is usually the more valuable of the two: a typical collector specimen runs about $35 against $10 for Peridotite, and premium Quartz can reach $250 or more.
About Peridotite
Peridotite is a coarse-grained ultramafic igneous rock composed predominantly of olivine along with varying amounts of pyroxene, making it the principal rock type of Earth's upper mantle. It is dense, dark green to black, and nearly devoid of quartz or feldspar, reflecting a chemical composition far more magnesium- and iron-rich than crustal rocks. Peridotite reaches the surface only through specific tectonic processes, since it normally resides tens of kilometers below the crust.
About Quartz
Quartz is silicon dioxide, SiO2, one of the most abundant minerals in Earth's continental crust, crystallizing in the trigonal division of the hexagonal crystal system with a hardness of 7 that makes it a standard reference point on the Mohs scale. Its six-sided prismatic crystals, often terminated by pyramidal points, are among the most recognizable crystal shapes in mineralogy. Quartz occurs in nearly every rock type and geologic setting, from granite pegmatites to sedimentary sandstones to hydrothermal veins.
Peridotite vs Quartz FAQ
Is Peridotite the same as Quartz?
No. Peridotite is a igneous rock while Quartz is a quartz family. Both sit near Mohs 5.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Peridotite from Quartz?
Both sit near Mohs 5.5–7, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Peridotite feels noticeably heavier for its size (specific gravity 3.1–3.4 versus 2.65 for Quartz). Hold a thin edge to the light: Peridotite is Opaque, Quartz is Transparent to translucent.
Which is harder, Peridotite or Quartz?
Quartz is harder: Mohs 7 against Mohs 5.5–7 for Peridotite.
Which is more valuable, Peridotite or Quartz?
Quartz is usually the more valuable of the two: a typical collector specimen runs about $35 against $10 for Peridotite, and premium Quartz can reach $250 or more.
