Igneous Rocks · common
Trachyte
Trachyte is a fine-grained volcanic rock rich in alkali feldspar. It is commonly gray, tan, pinkish, or brown and may show a rough or porphyritic texture.
Also known as: Trachyte porphyry, Alkali feldspar volcanic rock.
Trachyte properties at a glance
| Type | Igneous Rocks |
|---|---|
| Chemical formula | Alkali feldspar-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 | Light gray, Tan, Pink, Brown, Greenish gray, White |
| Rarity | common |
Geology & background
Forms when alkali feldspar-rich lava cools at or near the surface, often producing fine-grained or porphyritic volcanic texture.
Trachyte helps geologists identify alkali-rich volcanic rocks and volcanic equivalents of syenitic magmas.
How to identify Trachyte
- Look for light gray, tan, pinkish, or brown fine-grained volcanic texture.
- Feldspar phenocrysts can support trachyte when visible.
- Trachyte generally looks lighter and more feldspar-rich than basalt.
- It can overlap visually with rhyolite or andesite, so context helps.
Full Trachyte identification guide: checklist, home tests and look-alikes →
Trachyte vs similar stones
Not sure it isn't something else? Side-by-side comparisons with the stones most often confused with Trachyte.
Where Trachyte is found
Reported from multiple igneous terrains worldwide; verify locality against specimen provenance when available.
How much is Trachyte worth?
| Entry-level specimen | $1 |
|---|---|
| Typical collector specimen | $10 |
| Premium specimen | $75+ |
Trachyte 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
- Building stone in some regions
Interesting facts
- Trachyte is the volcanic counterpart of syenite.
- Its name refers to a rough texture seen in some specimens.
- Porphyritic trachyte can contain visible feldspar crystals in a fine groundmass.
Care & safety
Trachyte 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.
Trachyte FAQ
What is Trachyte?
Trachyte is a fine-grained volcanic rock rich in alkali feldspar. It is commonly gray, tan, pinkish, or brown and may show a rough or porphyritic texture.
How much is Trachyte worth?
Entry-level Trachyte specimens sell for around $1, a typical collector specimen for about $10, and premium pieces for $75 or more. Trachyte is usually valued for teaching, field context, locality, texture, color, mineral content, or unusually attractive specimens rather than high gem value.
How hard is Trachyte?
Trachyte 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 Trachyte used for?
Trachyte is used for field identification, volcanic rock comparison, education, and building stone in some regions.
