Comparison · Igneous Rocks
Basalt vs Tonalite
Basalt and Tonalite 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 Tonalite
- Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Streak color differs: Basalt leaves a variable; test individual minerals streak on unglazed porcelain, Tonalite leaves white to light gray.
- They overlap in black, gray, and green, but Tonalite also comes in white.
Basalt vs Tonalite properties
| Property | Basalt | Tonalite |
|---|---|---|
| Type | Igneous Rocks | Igneous Rocks |
| Mohs hardness | 6 | 6 |
| Luster | dull | dull |
| Streak | Variable; test individual minerals | White to light gray |
| Transparency | opaque | opaque |
| Specific gravity | 3 | 2.75 |
| Crystal system | varies | varies |
| Common colors | Black, Dark Gray, Dark Green | White, Gray, Black, Salt and pepper, Greenish gray |
| Rarity | common | common |
| Typical specimen value | $1–$30+ | $1–$75+ |
Which is more valuable?
Tonalite is usually the more valuable of the two: a typical collector specimen runs about $10 against $5 for Basalt, and premium Tonalite 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 Tonalite
Tonalite is a coarse-grained intrusive igneous rock rich in plagioclase and quartz, with less alkali feldspar than granite. It often looks gray, white, and black speckled.
Basalt vs Tonalite FAQ
Is Basalt the same as Tonalite?
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 Tonalite?
Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Streak color differs: Basalt leaves a variable; test individual minerals streak on unglazed porcelain, Tonalite leaves white to light gray. They overlap in black, gray, and green, but Tonalite also comes in white.
Which is harder, Basalt or Tonalite?
They are about equally hard, both near Mohs 6.
Which is more valuable, Basalt or Tonalite?
Tonalite is usually the more valuable of the two: a typical collector specimen runs about $10 against $5 for Basalt, and premium Tonalite can reach $75 or more.
