RocksdayAndesite vs Diorite
How to tell them apart
An intermediate volcanic rock typical of explosive volcanoes above subduction zones.
Photo: Photographer: Siim Sepp, 2005, CC BY-SA 3.0
A 'salt-and-pepper' coarse-grained rock of white plagioclase and black hornblende, between granite and gabbro in composition.
Photo: Michael C. Rygel, CC BY-SA 3.0
Key differences
- Diorite has the same composition but is entirely coarse-grained.
Side by side
| Property | Andesite | Diorite |
|---|---|---|
| Type | Igneous rock | Igneous rock |
| Mohs hardness | 6 | 6 |
| Luster | Dull | Granular |
| Colors | Gray | White, Black, Gray |
| Crystal system / structure | Porphyritic (crystals in fine groundmass) | Coarse-grained (phaneritic) |
| Specific gravity | 2.5–2.8 | 2.8–3 |
| Found in | The Andes; Cascade Range, USA | Guernsey, Channel Islands; Sierra Nevada, California |
Properties that are the same for both are grayed out.
How to identify andesite
- Medium gray.
- White feldspar crystals and dark specks scattered in a fine-grained base.
- Heavier than rhyolite, lighter than basalt.
- No visible quartz.
Structure: Porphyritic (crystals in fine groundmass)
Full Andesite guide →How to identify diorite
- Roughly equal white and black speckles.
- Coarse grains visible by eye.
- Little or no glassy quartz, no pink feldspar.
- Hard and heavy.
Structure: Coarse-grained (phaneritic)
Full Diorite guide →More comparisons
Could you tell them apart from a blurry close-up?
Play today's Rocksday