Comparison · Sedimentary Rocks
Arkose vs Graywacke
Arkose and Graywacke are easy to confuse because both are sedimentary rocks. Both sit near Mohs 6, 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 Arkose and Graywacke
- Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Streak color differs: Arkose leaves a variable; usually light-colored streak on unglazed porcelain, Graywacke leaves gray to dark gray.
- They overlap in brown and gray, but Arkose also comes in pink, red, and white and Graywacke also comes in green and black.
Arkose vs Graywacke properties
| Property | Arkose | Graywacke |
|---|---|---|
| Type | Sedimentary Rocks | Sedimentary Rocks |
| Mohs hardness | 6 | 6 |
| Luster | dull | dull |
| Streak | Variable; usually light-colored | Gray to dark gray |
| Transparency | opaque | opaque |
| Specific gravity | 2.45 | 2.55 |
| Crystal system | varies | varies |
| Common colors | Pink, Red, Tan, Gray, White | Dark gray, Greenish gray, Brown, Black |
| Rarity | common | common |
| Typical specimen value | $1–$75+ | $1–$75+ |
Which is more valuable?
Typical specimens of Arkose and Graywacke trade in a similar range, around $10.
About Arkose
Arkose is a feldspar-rich sandstone that often looks pink, reddish, tan, or light gray and may show visible sand-sized grains.
About Graywacke
Graywacke is a hard, dark, poorly sorted sandstone with a muddy matrix and mixed mineral or rock fragments.
Arkose vs Graywacke FAQ
Is Arkose the same as Graywacke?
No. Both are sedimentary rocks, but they are distinct rock types with different hardness, streak or luster. Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Arkose from Graywacke?
Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Streak color differs: Arkose leaves a variable; usually light-colored streak on unglazed porcelain, Graywacke leaves gray to dark gray. They overlap in brown and gray, but Arkose also comes in pink, red, and white and Graywacke also comes in green and black.
Which is harder, Arkose or Graywacke?
They are about equally hard, both near Mohs 6.
Which is more valuable, Arkose or Graywacke?
Typical specimens of Arkose and Graywacke trade in a similar range, around $10.
