Comparison · Feldspar Group vs Igneous Rocks
Feldspar vs Pegmatite
Feldspar and Pegmatite are easy to confuse. Both sit near Mohs 6–6.5, 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 Feldspar and Pegmatite
- Both sit near Mohs 6–6.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
- Hold a thin edge to the light: Feldspar is Transparent to translucent, Pegmatite is Opaque (individual crystals may be transparent).
- They overlap in pink and gray, but Feldspar also comes in green and clear and Pegmatite also comes in white and multicolored.
Feldspar vs Pegmatite properties
| Property | Feldspar | Pegmatite |
|---|---|---|
| Type | Feldspar Group | Igneous Rocks |
| Mohs hardness | 6–6.5 | 6–7 |
| Luster | Vitreous to pearly | Vitreous (large crystal faces) |
| Streak | White | — |
| Transparency | Transparent to translucent | Opaque (individual crystals may be transparent) |
| Specific gravity | 2.55–2.76 | 2.6–2.8 |
| Crystal system | Monoclinic to Triclinic (depending on species) | — |
| Common colors | White, Pink, Gray, Green (amazonite), Colorless | Pink, White, Gray, Multicolored (with tourmaline, etc.) |
| Rarity | common | common |
| Typical specimen value | $2–$150+ | $1–$75+ |
Which is more valuable?
Feldspar is usually the more valuable of the two: a typical collector specimen runs about $20 against $10 for Pegmatite, and premium Feldspar can reach $150 or more.
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.
About Pegmatite
Pegmatite is an exceptionally coarse-grained igneous rock, typically granitic in composition, distinguished by crystals often several centimeters to meters in size, far larger than in ordinary granite. Its unusually large crystals result from crystallizing out of a water- and rare-element-enriched residual melt left over after most of a magma body has already solidified. Pegmatites serve as the primary source of many rare minerals and gemstones, including tourmaline, beryl, spodumene, and topaz.
Feldspar vs Pegmatite FAQ
Is Feldspar the same as Pegmatite?
No. Feldspar is a feldspar group while Pegmatite is a igneous rock. Both sit near Mohs 6–6.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
How can you tell Feldspar from Pegmatite?
Both sit near Mohs 6–6.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Hold a thin edge to the light: Feldspar is Transparent to translucent, Pegmatite is Opaque (individual crystals may be transparent). They overlap in pink and gray, but Feldspar also comes in green and clear and Pegmatite also comes in white and multicolored.
Which is harder, Feldspar or Pegmatite?
They are about equally hard, both near Mohs 6–6.5.
Which is more valuable, Feldspar or Pegmatite?
Feldspar is usually the more valuable of the two: a typical collector specimen runs about $20 against $10 for Pegmatite, and premium Feldspar can reach $150 or more.
