Comparison · Igneous Rocks
Basalt vs Phonolite
Basalt and Phonolite 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 Phonolite
- 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, Phonolite leaves light gray to white.
- They overlap in black, gray, and green, but Phonolite also comes in brown and white.
Basalt vs Phonolite properties
| Property | Basalt | Phonolite |
|---|---|---|
| Type | Igneous Rocks | Igneous Rocks |
| Mohs hardness | 6 | 6 |
| Luster | dull | dull |
| Streak | Variable; test individual minerals | Light gray to white |
| Transparency | opaque | opaque |
| Specific gravity | 3 | 2.6 |
| Crystal system | varies | varies |
| Common colors | Black, Dark Gray, Dark Green | Gray, Greenish gray, Brown, Black, White |
| Rarity | common | uncommon |
| Typical specimen value | $1–$30+ | $1–$75+ |
Which is more valuable?
Phonolite is usually the more valuable of the two: a typical collector specimen runs about $10 against $5 for Basalt, and premium Phonolite 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 Phonolite
Phonolite is an alkali-rich volcanic rock, often gray to greenish gray and fine-grained. Some pieces ring when struck, which inspired the name.
Basalt vs Phonolite FAQ
Is Basalt the same as Phonolite?
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 Phonolite?
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, Phonolite leaves light gray to white. They overlap in black, gray, and green, but Phonolite also comes in brown and white.
Which is harder, Basalt or Phonolite?
They are about equally hard, both near Mohs 6.
Which is more valuable, Basalt or Phonolite?
Phonolite is usually the more valuable of the two: a typical collector specimen runs about $10 against $5 for Basalt, and premium Phonolite can reach $75 or more.
