Igneous Rocks · common
Tonalite
Tonalite is a coarse-grained intrusive igneous rock rich in plagioclase and quartz, with less alkali feldspar than granite. It often looks gray, white, and black speckled.
Also known as: Quartz diorite, Plagioclase-rich intrusive rock.
Tonalite properties at a glance
| Type | Igneous Rocks |
|---|---|
| Chemical formula | Quartz and plagioclase-rich intrusive rock |
| Mohs hardness | 6 |
| Luster | dull |
| Streak | White to light gray |
| Cleavage | Variable by feldspar grains |
| Fracture | Uneven to granular |
| Specific gravity | 2.75 |
| Transparency | opaque |
| Common colors | White, Gray, Black, Salt and pepper, Greenish gray |
| Rarity | common |
Geology & background
Forms when quartz-bearing magma cools slowly underground, producing coarse plagioclase-rich crystals with dark mafic minerals.
Tonalite helps geologists classify intrusive rocks and study continental crust formation.
How to identify Tonalite
- Look for coarse gray-white-black texture with quartz and abundant plagioclase.
- Tonalite has less pink alkali feldspar than many granites.
- It can sit visually between diorite and granodiorite.
- A close photo of grain mix helps avoid overcalling granite.
Full Tonalite identification guide: checklist, home tests and look-alikes →
Tonalite vs similar stones
Not sure it isn't something else? Side-by-side comparisons with the stones most often confused with Tonalite.
Where Tonalite is found
Reported from multiple igneous terrains worldwide; verify locality against specimen provenance when available.
How much is Tonalite worth?
| Entry-level specimen | $1 |
|---|---|
| Typical collector specimen | $10 |
| Premium specimen | $75+ |
Tonalite is usually valued for teaching, field context, locality, texture, color, mineral content, or unusually attractive specimens rather than high gem value.
Common uses
- Field identification
- Education
- Intrusive rock comparison
- Building stone when suitable
Interesting facts
- Tonalite is part of the tonalite-trondhjemite-granodiorite family important in ancient crust.
- It can resemble granodiorite, diorite, or granite in hand sample.
- Plagioclase is the dominant feldspar.
Care & safety
Tonalite can vary in toughness, porosity, vesicles, glass content, and weathering depending on cooling history and mineral mix.
Avoid inhaling dust. Do not cut, grind, or polish unknown igneous rocks without eye protection and a properly rated respirator.
Tonalite FAQ
What is Tonalite?
Tonalite is a coarse-grained intrusive igneous rock rich in plagioclase and quartz, with less alkali feldspar than granite. It often looks gray, white, and black speckled.
How much is Tonalite worth?
Entry-level Tonalite specimens sell for around $1, a typical collector specimen for about $10, and premium pieces for $75 or more. Tonalite is usually valued for teaching, field context, locality, texture, color, mineral content, or unusually attractive specimens rather than high gem value.
How hard is Tonalite?
Tonalite has a Mohs hardness of 6. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
What is Tonalite used for?
Tonalite is used for field identification, education, intrusive rock comparison, and building stone when suitable.
