Igneous Rocks · uncommon
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.
Also known as: Sound stone, Alkali volcanic rock.
Phonolite properties at a glance
| Type | Igneous Rocks |
|---|---|
| Chemical formula | Alkali feldspar and feldspathoid-rich volcanic rock |
| Mohs hardness | 6 |
| Luster | dull |
| Streak | Light gray to white |
| Cleavage | None to variable by phenocrysts |
| Fracture | Uneven to conchoidal |
| Specific gravity | 2.6 |
| Transparency | opaque |
| Common colors | Gray, Greenish gray, Brown, Black, White |
| Rarity | uncommon |
Geology & background
Forms when silica-undersaturated, alkali-rich lava cools at or near the surface, commonly producing fine-grained volcanic rock with feldspathoid minerals.
Phonolite helps geologists identify alkali-rich volcanic settings and silica-undersaturated magmas.
How to identify Phonolite
- Look for gray to greenish gray fine-grained volcanic texture.
- Phonolite can be hard to confirm from photos unless locality or mineral context supports it.
- It usually lacks obvious quartz.
- Do not confuse it with ordinary basalt or andesite without alkali-rock clues.
Full Phonolite identification guide: checklist, home tests and look-alikes →
Phonolite vs similar stones
Not sure it isn't something else? Side-by-side comparisons with the stones most often confused with Phonolite.
Where Phonolite is found
Reported from multiple igneous terrains worldwide; verify locality against specimen provenance when available.
How much is Phonolite worth?
| Entry-level specimen | $1 |
|---|---|
| Typical collector specimen | $10 |
| Premium specimen | $75+ |
Phonolite is usually valued for teaching, field context, locality, texture, color, mineral content, or unusually attractive specimens rather than high gem value.
Common uses
- Field identification
- Volcanic rock comparison
- Education
- Collector specimens
Interesting facts
- The name phonolite means sound stone.
- It is the volcanic counterpart of nepheline syenite.
- Feldspathoid minerals such as nepheline can be important in phonolite.
Care & safety
Phonolite can vary in toughness, porosity, vesicles, glass content, and weathering depending on cooling history and mineral mix.
Avoid inhaling dust. Do not cut, grind, or polish unknown igneous rocks without eye protection and a properly rated respirator.
Phonolite FAQ
What is 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.
How much is Phonolite worth?
Entry-level Phonolite specimens sell for around $1, a typical collector specimen for about $10, and premium pieces for $75 or more. Phonolite is usually valued for teaching, field context, locality, texture, color, mineral content, or unusually attractive specimens rather than high gem value.
How hard is Phonolite?
Phonolite has a Mohs hardness of 6. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
What is Phonolite used for?
Phonolite is used for field identification, volcanic rock comparison, education, and collector specimens.
