Comparison · Sedimentary Rocks vs Quartz Family
Graywacke vs Quartz
Graywacke and Quartz are easy to confuse. Quartz is harder (Mohs 7) than Graywacke (Mohs 6), so Quartz will scratch Graywacke and not the other way round. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Graywacke and Quartz
- Quartz is harder (Mohs 7) than Graywacke (Mohs 6), so Quartz will scratch Graywacke and not the other way round. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
- Streak color differs: Graywacke leaves a gray to dark gray streak on unglazed porcelain, Quartz leaves white.
- Luster is different: Graywacke is dull while Quartz is vitreous, greasy on fracture surfaces.
- Hold a thin edge to the light: Graywacke is opaque, Quartz is Transparent to translucent.
- They overlap in gray, brown, and black, but Graywacke also comes in green and Quartz also comes in clear, purple, yellow, and pink.
Graywacke vs Quartz properties
| Property | Graywacke | Quartz |
|---|---|---|
| Type | Sedimentary Rocks | Quartz Family |
| Mohs hardness | 6 | 7 |
| Luster | dull | Vitreous, greasy on fracture surfaces |
| Streak | Gray to dark gray | White |
| Transparency | opaque | Transparent to translucent |
| Specific gravity | 2.55 | 2.65 |
| Crystal system | varies | Trigonal |
| Common colors | Dark gray, Greenish gray, Brown, Black | Colorless, White, Purple (amethyst), Yellow (citrine), Pink (rose), Brown/black (smoky) |
| Rarity | common | common |
| Typical specimen value | $1–$75+ | $5–$250+ |
Which is more valuable?
Quartz is usually the more valuable of the two: a typical collector specimen runs about $35 against $10 for Graywacke, and premium Quartz can reach $250 or more.
About Graywacke
Graywacke is a hard, dark, poorly sorted sandstone with a muddy matrix and mixed mineral or rock fragments.
About Quartz
Quartz is silicon dioxide, SiO2, one of the most abundant minerals in Earth's continental crust, crystallizing in the trigonal division of the hexagonal crystal system with a hardness of 7 that makes it a standard reference point on the Mohs scale. Its six-sided prismatic crystals, often terminated by pyramidal points, are among the most recognizable crystal shapes in mineralogy. Quartz occurs in nearly every rock type and geologic setting, from granite pegmatites to sedimentary sandstones to hydrothermal veins.
Graywacke vs Quartz FAQ
Is Graywacke the same as Quartz?
No. Graywacke is a sedimentary rock while Quartz is a quartz family. Quartz is harder (Mohs 7) than Graywacke (Mohs 6), so Quartz will scratch Graywacke and not the other way round. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
How can you tell Graywacke from Quartz?
Quartz is harder (Mohs 7) than Graywacke (Mohs 6), so Quartz will scratch Graywacke and not the other way round. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. Streak color differs: Graywacke leaves a gray to dark gray streak on unglazed porcelain, Quartz leaves white. Luster is different: Graywacke is dull while Quartz is vitreous, greasy on fracture surfaces.
Which is harder, Graywacke or Quartz?
Quartz is harder: Mohs 7 against Mohs 6 for Graywacke.
Which is more valuable, Graywacke or Quartz?
Quartz is usually the more valuable of the two: a typical collector specimen runs about $35 against $10 for Graywacke, and premium Quartz can reach $250 or more.
