Comparison · Feldspar Group vs Igneous Rocks
Feldspar vs Tuff
Feldspar and Tuff are easy to confuse. Feldspar is harder (Mohs 6–6.5) than Tuff (Mohs 2–5), so Feldspar will scratch Tuff and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Feldspar and Tuff
- Feldspar is harder (Mohs 6–6.5) than Tuff (Mohs 2–5), so Feldspar will scratch Tuff and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
- Feldspar feels noticeably heavier for its size (specific gravity 2.55–2.76 versus 1.5–2.7 for Tuff).
- Hold a thin edge to the light: Feldspar is Transparent to translucent, Tuff is Opaque.
- They overlap in pink, gray, and green, but Feldspar also comes in clear and Tuff also comes in brown and white.
Feldspar vs Tuff properties
| Property | Feldspar | Tuff |
|---|---|---|
| Type | Feldspar Group | Igneous Rocks |
| Mohs hardness | 6–6.5 | 2–5 |
| Luster | Vitreous to pearly | Dull to earthy; glassy shards may show vitreous luster |
| Streak | White | — |
| Transparency | Transparent to translucent | Opaque |
| Specific gravity | 2.55–2.76 | 1.5–2.7 |
| Crystal system | Monoclinic to Triclinic (depending on species) | — |
| Common colors | White, Pink, Gray, Green (amazonite), Colorless | Light gray, Tan, Pink, Greenish, White |
| 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 Tuff, 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 Tuff
Tuff is a volcanic rock formed from compacted and cemented volcanic ash ejected during explosive eruptions, distinguishing it from lava-derived rocks like basalt or andesite that solidify directly from molten flow. Its texture ranges from soft and crumbly to dense and welded, depending on how hot the ash was when it settled and how much compaction it underwent afterward. Tuff deposits can blanket enormous areas following a single major eruption, preserving a snapshot of that eruption's ash fall in the rock record.
Feldspar vs Tuff FAQ
Is Feldspar the same as Tuff?
No. Feldspar is a feldspar group while Tuff is a igneous rock. Feldspar is harder (Mohs 6–6.5) than Tuff (Mohs 2–5), so Feldspar will scratch Tuff and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
How can you tell Feldspar from Tuff?
Feldspar is harder (Mohs 6–6.5) than Tuff (Mohs 2–5), so Feldspar will scratch Tuff and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Feldspar feels noticeably heavier for its size (specific gravity 2.55–2.76 versus 1.5–2.7 for Tuff). Hold a thin edge to the light: Feldspar is Transparent to translucent, Tuff is Opaque.
Which is harder, Feldspar or Tuff?
Feldspar is harder: Mohs 6–6.5 against Mohs 2–5 for Tuff.
Which is more valuable, Feldspar or Tuff?
Feldspar is usually the more valuable of the two: a typical collector specimen runs about $20 against $10 for Tuff, and premium Feldspar can reach $150 or more.
