RocksdayGneiss vs Mylonite
How to tell them apart
A high-grade metamorphic rock with bold light and dark bands, formed under intense heat and pressure.
Photo: No machine-readable author provided. Siim assumed (based on copyright claims)., CC BY-SA 3.0
A fine-grained, streaky rock formed deep in fault zones where rocks flow instead of breaking.
Photo: Unknown, CC BY-SA 1.0
Key differences
- Gneiss is coarser with clear bands.
Side by side
| Property | Gneiss | Mylonite |
|---|---|---|
| Type | Metamorphic rock | Metamorphic rock |
| Mohs hardness | 6–7 | 6–7 |
| Luster | Granular | Dull to silky |
| Colors | Gray, White, Black, Pink | Gray, Black, Green |
| Crystal system / structure | Coarse, banded | Fine-grained, streaky (sheared) |
| Specific gravity | 2.6–2.9 | 2.6–2.9 |
| Found in | Acasta River, Canada; Outer Hebrides, Scotland | Moine Thrust, Scotland; Alpine Fault, New Zealand |
Properties that are the same for both are grayed out.
How to identify gneiss
- Alternating light and dark bands, often wavy.
- Coarse, visible grains.
- Hard; doesn't split into sheets.
- Bands may be folded.
Structure: Coarse, banded
Full Gneiss guide →How to identify mylonite
- Fine streaks and stretched grains.
- Larger crystals smeared into 'eyes'.
- Found along major faults.
Structure: Fine-grained, streaky (sheared)
Full Mylonite guide →More comparisons
Could you tell them apart from a blurry close-up?
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