Comparison · Quartz Family vs Igneous Rocks
Quartz vs Scoria
Quartz and Scoria are easy to confuse. Quartz is harder (Mohs 7) than Scoria (Mohs 5–6), so Quartz will scratch Scoria 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 Quartz and Scoria
- Quartz is harder (Mohs 7) than Scoria (Mohs 5–6), so Quartz will scratch Scoria 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.
- Quartz feels noticeably heavier for its size (specific gravity 2.65 versus 1.5–2.6 for Scoria).
- Hold a thin edge to the light: Quartz is Transparent to translucent, Scoria is Opaque.
- They overlap in black and brown, but Quartz also comes in clear, purple, yellow, pink, and gray and Scoria also comes in red.
Quartz vs Scoria properties
| Property | Quartz | Scoria |
|---|---|---|
| Type | Quartz Family | Igneous Rocks |
| Mohs hardness | 7 | 5–6 |
| Luster | Vitreous, greasy on fracture surfaces | Dull, glassy |
| Streak | White | — |
| Transparency | Transparent to translucent | Opaque |
| Specific gravity | 2.65 | 1.5–2.6 |
| Crystal system | Trigonal | — |
| Common colors | Colorless, White, Purple (amethyst), Yellow (citrine), Pink (rose), Brown/black (smoky) | Dark red, Black, Brown, Reddish brown |
| Rarity | common | common |
| Typical specimen value | $5–$250+ | $1–$75+ |
Which is more valuable?
Quartz is usually the more valuable of the two: a typical collector specimen runs about $35 against $10 for Scoria, and premium Quartz can reach $250 or more.
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.
About Scoria
Scoria is a dark, highly vesicular volcanic rock of basaltic to andesitic composition, riddled with gas bubbles trapped as the lava cooled and depressurized rapidly. It is denser and darker than pumice, containing thicker vesicle walls and less silica, which is why scoria typically sinks in water while pumice floats. Its red color, when present, comes from oxidized iron in the rock.
Quartz vs Scoria FAQ
Is Quartz the same as Scoria?
No. Quartz is a quartz family while Scoria is a igneous rock. Quartz is harder (Mohs 7) than Scoria (Mohs 5–6), so Quartz will scratch Scoria 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 Quartz from Scoria?
Quartz is harder (Mohs 7) than Scoria (Mohs 5–6), so Quartz will scratch Scoria 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. Quartz feels noticeably heavier for its size (specific gravity 2.65 versus 1.5–2.6 for Scoria). Hold a thin edge to the light: Quartz is Transparent to translucent, Scoria is Opaque.
Which is harder, Quartz or Scoria?
Quartz is harder: Mohs 7 against Mohs 5–6 for Scoria.
Which is more valuable, Quartz or Scoria?
Quartz is usually the more valuable of the two: a typical collector specimen runs about $35 against $10 for Scoria, and premium Quartz can reach $250 or more.
