Comparison · Igneous Rocks
Anorthosite vs Gabbro
Anorthosite and Gabbro are easy to confuse because both are igneous rocks. Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Anorthosite and Gabbro
- Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Luster is different: Anorthosite is pearly while Gabbro is dull to vitreous (in crystals).
- Hold a thin edge to the light: Anorthosite is opaque, Gabbro is Opaque.
- They overlap in white, gray, and black, but Anorthosite also comes in blue and pink and Gabbro also comes in green and multicolored.
Anorthosite vs Gabbro properties
| Property | Anorthosite | Gabbro |
|---|---|---|
| Type | Igneous Rocks | Igneous Rocks |
| Mohs hardness | 6 | 5–6.5 |
| Luster | pearly | Dull to vitreous (in crystals) |
| Streak | White to pale gray | — |
| Transparency | opaque | Opaque |
| Specific gravity | 2.75 | 2.9–3.1 |
| Crystal system | varies | — |
| Common colors | White, Gray, Blue gray, Black, Pale pink | Dark gray, Black, Greenish black, Speckled black and white |
| Rarity | common | common |
| Typical specimen value | $1–$75+ | $1–$75+ |
Which is more valuable?
Typical specimens of Anorthosite and Gabbro trade in a similar range, around $10.
About Anorthosite
Anorthosite is a coarse-grained igneous rock made mostly of plagioclase feldspar. It often looks light gray to white, sometimes with dark mafic minerals or bluish feldspar flashes.
About Gabbro
Gabbro is a coarse-grained, dark-colored intrusive igneous rock composed mainly of calcium-rich plagioclase feldspar and pyroxene, with the plutonic equivalent of basalt. It forms deep underground where mafic magma cools slowly enough for its mineral grains to grow large and interlock visibly. Its dense, speckled black-and-white texture makes it a popular dimension stone sold commercially as black granite.
Anorthosite vs Gabbro FAQ
Is Anorthosite the same as Gabbro?
No. Both are igneous rocks, but they are distinct rock types with different hardness, streak or luster. Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Anorthosite from Gabbro?
Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Luster is different: Anorthosite is pearly while Gabbro is dull to vitreous (in crystals). Hold a thin edge to the light: Anorthosite is opaque, Gabbro is Opaque.
Which is harder, Anorthosite or Gabbro?
They are about equally hard, both near Mohs 6.
Which is more valuable, Anorthosite or Gabbro?
Typical specimens of Anorthosite and Gabbro trade in a similar range, around $10.
