Comparison · Igneous Rocks vs Feldspar Group
Anorthosite vs Feldspar
Anorthosite and Feldspar are easy to confuse. 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 Feldspar
- Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Streak color differs: Anorthosite leaves a white to pale gray streak on unglazed porcelain, Feldspar leaves white.
- Luster is different: Anorthosite is pearly while Feldspar is vitreous to pearly.
- Hold a thin edge to the light: Anorthosite is opaque, Feldspar is Transparent to translucent.
- They overlap in gray and pink, but Anorthosite also comes in white, blue, and black and Feldspar also comes in green and clear.
Anorthosite vs Feldspar properties
| Property | Anorthosite | Feldspar |
|---|---|---|
| Type | Igneous Rocks | Feldspar Group |
| Mohs hardness | 6 | 6–6.5 |
| Luster | pearly | Vitreous to pearly |
| Streak | White to pale gray | White |
| Transparency | opaque | Transparent to translucent |
| Specific gravity | 2.75 | 2.55–2.76 |
| Crystal system | varies | Monoclinic to Triclinic (depending on species) |
| Common colors | White, Gray, Blue gray, Black, Pale pink | White, Pink, Gray, Green (amazonite), Colorless |
| Rarity | common | common |
| Typical specimen value | $1–$75+ | $2–$150+ |
Which is more valuable?
Feldspar is usually the more valuable of the two: a typical collector specimen runs about $20 against $10 for Anorthosite, and premium Feldspar can reach $150 or more.
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 Feldspar
Feldspar is not a single mineral but a group of related aluminosilicate minerals, comprising the potassium feldspars, orthoclase, microcline, and sanidine, and the plagioclase series running from albite to anorthite, together making up roughly 60 percent of Earth's crust by volume. All share a similar framework silicate structure, two cleavage directions near 90 degrees, and moderate hardness, but differ in composition, color, and crystal system. As the most abundant mineral group on the planet, feldspar defines granite, basalt, gneiss, and countless other rock types.
Anorthosite vs Feldspar FAQ
Is Anorthosite the same as Feldspar?
No. Anorthosite is a igneous rock while Feldspar is a feldspar group. 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 Feldspar?
Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Streak color differs: Anorthosite leaves a white to pale gray streak on unglazed porcelain, Feldspar leaves white. Luster is different: Anorthosite is pearly while Feldspar is vitreous to pearly.
Which is harder, Anorthosite or Feldspar?
They are about equally hard, both near Mohs 6.
Which is more valuable, Anorthosite or Feldspar?
Feldspar is usually the more valuable of the two: a typical collector specimen runs about $20 against $10 for Anorthosite, and premium Feldspar can reach $150 or more.
