Comparison · Igneous Rocks
Andesite vs Porphyry
Andesite and Porphyry are easy to confuse because both are igneous rocks. Both sit near Mohs 5–6, 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 Andesite and Porphyry
- Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- They overlap in gray and green, but Andesite also comes in brown and black and Porphyry also comes in purple and red.
Andesite vs Porphyry properties
| Property | Andesite | Porphyry |
|---|---|---|
| Type | Igneous Rocks | Igneous Rocks |
| Mohs hardness | 5–6 | 5–7 |
| Luster | Dull groundmass with vitreous phenocrysts | Dull to vitreous |
| Transparency | Opaque | Opaque |
| Specific gravity | 2.5–2.8 | 2.6–2.8 |
| Common colors | Gray, Dark gray, Greenish gray, Brown, Black | Purple, Red, Gray, Green |
| Rarity | common | common |
| Typical specimen value | $1–$75+ | $1–$75+ |
Which is more valuable?
Typical specimens of Andesite and Porphyry trade in a similar range, around $10.
About Andesite
Andesite is a fine-grained, intermediate volcanic rock formed from lava with a silica content between basalt and rhyolite, typically 57 to 63 percent. It is named for the Andes Mountains, where it makes up much of the volcanic arc, and its groundmass is usually too fine to identify individual minerals without magnification. Andesite forms at convergent plate boundaries where oceanic crust melts beneath continental or island arcs.
About Porphyry
Porphyry is a textural term for any igneous rock that contains large, visible crystals called phenocrysts embedded in a much finer-grained groundmass, rather than a description of a specific mineral composition. The texture records a two-stage cooling history, slow crystal growth at depth followed by rapid cooling near or at the surface. Porphyry can be volcanic or shallow intrusive and of almost any composition, from basaltic to rhyolitic.
Andesite vs Porphyry FAQ
Is Andesite the same as Porphyry?
No. Both are igneous rocks, but they are distinct rock types with different hardness, streak or luster. Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Andesite from Porphyry?
Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. They overlap in gray and green, but Andesite also comes in brown and black and Porphyry also comes in purple and red.
Which is harder, Andesite or Porphyry?
Porphyry is harder: Mohs 5–7 against Mohs 5–6 for Andesite.
Which is more valuable, Andesite or Porphyry?
Typical specimens of Andesite and Porphyry trade in a similar range, around $10.
