Comparison · Igneous Rocks
Basalt vs Diabase
Basalt and Diabase are easy to confuse because both are igneous 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 Basalt and Diabase
- Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Luster is different: Basalt is dull while Diabase is varies.
Basalt vs Diabase properties
| Property | Basalt | Diabase |
|---|---|---|
| Type | Igneous Rocks | Igneous Rocks |
| Mohs hardness | 6 | 6 |
| Luster | dull | varies |
| Streak | Variable; test individual minerals | Variable; test individual minerals |
| Transparency | opaque | opaque |
| Specific gravity | 3 | 2.8 |
| Crystal system | varies | varies |
| Common colors | Black, Dark Gray, Dark Green | Various |
| Rarity | common | common |
| Typical specimen value | $1–$30+ | $1–$75+ |
Which is more valuable?
Diabase is usually the more valuable of the two: a typical collector specimen runs about $10 against $5 for Basalt, and premium Diabase can reach $75 or more.
About Basalt
Basalt is a dark, fine-grained volcanic rock that makes up most of the ocean floor and Hawaiian Islands. It often forms distinctive columnar jointing.
About Diabase
Diabase is a dark, medium-grained mafic igneous rock, also called dolerite in many regions. It commonly forms in dikes and sills and sits texturally between basalt and gabbro.
Basalt vs Diabase FAQ
Is Basalt the same as Diabase?
No. Both are igneous 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 Basalt from Diabase?
Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Luster is different: Basalt is dull while Diabase is varies.
Which is harder, Basalt or Diabase?
They are about equally hard, both near Mohs 6.
Which is more valuable, Basalt or Diabase?
Diabase is usually the more valuable of the two: a typical collector specimen runs about $10 against $5 for Basalt, and premium Diabase can reach $75 or more.
