RocksdayGranite vs Porphyry
How to tell them apart
A coarse-grained rock that cooled slowly deep underground, made of quartz, feldspar and mica or hornblende.
Photo: The stone gate, CC BY-SA 4.0
Any igneous rock with large crystals floating in a fine-grained background.
Photo: James St. John, CC BY 2.0
Key differences
- Granite's grains are all coarse.
Side by side
| Property | Granite | Porphyry |
|---|---|---|
| Type | Igneous rock | Igneous rock |
| Mohs hardness | 6–7 | 6–6.5 |
| Luster | Granular, sparkly | Dull to polished |
| Colors | Pink, Gray, White, Black | Purple, Red, Gray, Green |
| Crystal system / structure | Coarse-grained (phaneritic) | Porphyritic (large crystals in fine groundmass) |
| Specific gravity | 2.63–2.75 | 2.6–2.8 |
| Found in | Sierra Nevada, California; Stone Mountain, Georgia | Eastern Desert, Egypt; Älvdalen, Sweden |
Properties that are the same for both are grayed out.
How to identify granite
- Speckled with interlocking grains you can see without a lens.
- Glassy gray quartz plus pink or white blocky feldspar.
- Black specks of mica or hornblende.
- Hard, with no layering or banding.
Structure: Coarse-grained (phaneritic)
Full Granite guide →How to identify porphyry
- Distinct larger crystals scattered through a fine matrix.
- Often purple, red or green.
- Takes a high polish.
Structure: Porphyritic (large crystals in fine groundmass)
Full Porphyry guide →More comparisons
Could you tell them apart from a blurry close-up?
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