Comparison · Metamorphic Rocks vs Quartz Family
Mylonite vs Quartz
Mylonite and Quartz are easy to confuse. Quartz is harder (Mohs 7) than Mylonite (Mohs 5.5), so Quartz will scratch Mylonite 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 Mylonite and Quartz
- Quartz is harder (Mohs 7) than Mylonite (Mohs 5.5), so Quartz will scratch Mylonite 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: Mylonite leaves a variable by mineral content streak on unglazed porcelain, Quartz leaves white.
- Luster is different: Mylonite is silky while Quartz is vitreous, greasy on fracture surfaces.
- Hold a thin edge to the light: Mylonite is opaque, Quartz is Transparent to translucent.
- They overlap in gray, black, and brown, but Mylonite also comes in white and green and Quartz also comes in clear, purple, yellow, and pink.
Mylonite vs Quartz properties
| Property | Mylonite | Quartz |
|---|---|---|
| Type | Metamorphic Rocks | Quartz Family |
| Mohs hardness | 5.5 | 7 |
| Luster | silky | Vitreous, greasy on fracture surfaces |
| Streak | Variable by mineral content | White |
| Transparency | opaque | Transparent to translucent |
| Specific gravity | 2.7 | 2.65 |
| Crystal system | varies | Trigonal |
| Common colors | Gray, Black, White, Green, Brown | Colorless, White, Purple (amethyst), Yellow (citrine), Pink (rose), Brown/black (smoky) |
| Rarity | uncommon | 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 Mylonite, and premium Quartz can reach $250 or more.
About Mylonite
Mylonite is a fine-grained, streaky metamorphic rock formed by intense ductile shearing in fault zones. It can show stretched mineral bands and a strong fabric.
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.
Mylonite vs Quartz FAQ
Is Mylonite the same as Quartz?
No. Mylonite is a metamorphic rock while Quartz is a quartz family. Quartz is harder (Mohs 7) than Mylonite (Mohs 5.5), so Quartz will scratch Mylonite 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 Mylonite from Quartz?
Quartz is harder (Mohs 7) than Mylonite (Mohs 5.5), so Quartz will scratch Mylonite 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: Mylonite leaves a variable by mineral content streak on unglazed porcelain, Quartz leaves white. Luster is different: Mylonite is silky while Quartz is vitreous, greasy on fracture surfaces.
Which is harder, Mylonite or Quartz?
Quartz is harder: Mohs 7 against Mohs 5.5 for Mylonite.
Which is more valuable, Mylonite or Quartz?
Quartz is usually the more valuable of the two: a typical collector specimen runs about $35 against $10 for Mylonite, and premium Quartz can reach $250 or more.
