Comparison · Metamorphic Rocks
Hornfels vs Skarn
Hornfels and Skarn are easy to confuse because both are metamorphic 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 Hornfels and Skarn
- Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Streak color differs: Hornfels leaves a variable; usually pale gray streak on unglazed porcelain, Skarn leaves variable by mineral content.
Hornfels vs Skarn properties
| Property | Hornfels | Skarn |
|---|---|---|
| Type | Metamorphic Rocks | Metamorphic Rocks |
| Mohs hardness | 6 | 5.5 |
| Luster | dull | dull |
| Streak | Variable; usually pale gray | Variable by mineral content |
| Transparency | opaque | opaque |
| Specific gravity | 2.7 | 3.1 |
| Crystal system | varies | varies |
| Common colors | Gray, Black, Brown, Green, Red, White | Green, Brown, White, Gray, Red, Black |
| Rarity | common | uncommon |
| Typical specimen value | $1–$75+ | $2–$150+ |
Which is more valuable?
Skarn is usually the more valuable of the two: a typical collector specimen runs about $20 against $10 for Hornfels, and premium Skarn can reach $150 or more.
About Hornfels
Hornfels is a hard, dense, fine-grained contact metamorphic rock. It often looks dark, tough, and baked, with little visible layering.
About Skarn
Skarn is a calc-silicate metamorphic rock formed where hot intrusive fluids alter carbonate rocks. It can be green, brown, white, red, or mixed and may contain garnet, pyroxene, epidote, or ore minerals.
Hornfels vs Skarn FAQ
Is Hornfels the same as Skarn?
No. Both are metamorphic 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 Hornfels from Skarn?
Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Streak color differs: Hornfels leaves a variable; usually pale gray streak on unglazed porcelain, Skarn leaves variable by mineral content.
Which is harder, Hornfels or Skarn?
Hornfels is harder: Mohs 6 against Mohs 5.5 for Skarn.
Which is more valuable, Hornfels or Skarn?
Skarn is usually the more valuable of the two: a typical collector specimen runs about $20 against $10 for Hornfels, and premium Skarn can reach $150 or more.
