RocksdayDiorite vs Granodiorite
How to tell them apart
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
A gray, granite-like rock with more white plagioclase than granite — the most common rock of continental crust.
Photo: Rudolf Pohl, CC BY-SA 3.0
Key differences
- Diorite has little or no quartz.
Side by side
| Property | Diorite | Granodiorite |
|---|---|---|
| Type | Igneous rock | Igneous rock |
| Mohs hardness | 6 | 6–7 |
| Luster | Granular | Granular |
| Colors | White, Black, Gray | Gray, White, Black |
| Crystal system / structure | Coarse-grained (phaneritic) | Coarse-grained (phaneritic) |
| Specific gravity | 2.8–3 | 2.7–2.8 |
| Found in | Guernsey, Channel Islands; Sierra Nevada, California | Half Dome, Yosemite; Coast Mountains, British Columbia |
Properties that are the same for both are grayed out.
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 →How to identify granodiorite
- Salt-and-pepper gray with some glassy quartz.
- Mostly white plagioclase, little pink feldspar.
- Coarse, even grains.
Structure: Coarse-grained (phaneritic)
Full Granodiorite guide →More comparisons
Could you tell them apart from a blurry close-up?
Play today's Rocksday