RocksdayDiorite vs Tonalite
To tell Diorite from Tonalite: Diorite has little or no quartz.
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 coarse intrusive rock of quartz and plagioclase with almost no potassium feldspar. It looks like a gray granite.
Photo: Ingwik, Public domain
Key differences
- Diorite has little or no quartz.
Side by side
| Property | Diorite | Tonalite |
|---|---|---|
| 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 | 2.6–2.8 |
| Found in | Guernsey, Channel Islands; Sierra Nevada, California | Tonale Pass, Italy; Coastal Batholith, Peru |
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 tonalite
- Gray, speckled, with glassy quartz.
- Feldspar is white plagioclase, not pink alkali feldspar.
- Dark grains of hornblende or biotite.
Structure: Coarse-grained (phaneritic)
Full Tonalite guide →More comparisons
Frequently asked questions
What is the difference between diorite and tonalite?
Diorite is an igneous rock with a Mohs hardness of about 6 and a granular luster, usually white, black or gray. Tonalite is an igneous rock with a Mohs hardness of about 6–7 and a granular luster, usually gray, white or black.
How can you tell diorite from tonalite?
Diorite has little or no quartz.
Could you tell them apart from a blurry close-up?
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