RocksdayBlueschist vs Glaucophane
The quickest way to tell Blueschist from Glaucophane: Blueschist is a rock — a mix of grains or minerals; Glaucophane is a single mineral.
A rare blue-gray rock formed at high pressure but low temperature in subduction zones.
Photo: Shannon Heinle, CC0
The blue amphibole that colors blueschist, formed when ocean crust is dragged to depth and stays cool.
Photo: Didier Descouens, CC BY-SA 4.0
Quick tests
- Texture: Blueschist is a rock — a mix of grains or minerals; Glaucophane is a single mineral.
Key differences
- Blueschist is the rock; glaucophane is the blue mineral in it.
Side by side
| Property | Blueschist | Glaucophane |
|---|---|---|
| Type | Metamorphic rock | Mineral |
| Mohs hardness | 5–6 | 6–6.5 |
| Luster | Silky to dull | Vitreous to silky |
| Streak | — | Gray |
| Colors | Blue, Gray | Blue, Gray |
| Crystal system / structure | Foliated, glaucophane-rich | Monoclinic |
| Specific gravity | 3–3.2 | 3–3.2 |
| Formula | — | Na₂(Mg₃Al₂)Si₈O₂₂(OH)₂ |
| Found in | Franciscan Complex, California; Syros, Greece | Île de Groix, France; Franciscan Complex, California |
Properties that are the same for both are grayed out.
How to identify blueschist
- Lavender to blue-gray color.
- Foliated, sometimes with red garnets.
- Found in old subduction zones.
Structure: Foliated, glaucophane-rich
Full Blueschist guide →How to identify glaucophane
- Blue blades or fibrous patches in a tough metamorphic rock.
- Two amphibole cleavages.
- Hardness about 6.
Crystal system: Monoclinic
Full Glaucophane guide →More comparisons
Frequently asked questions
What is the difference between blueschist and glaucophane?
Blueschist is a metamorphic rock with a Mohs hardness of about 5–6 and a silky to dull luster, usually blue or gray. Glaucophane is a mineral with a Mohs hardness of 6–6.5 and a vitreous to silky luster, usually blue or gray.
How can you tell blueschist from glaucophane?
Blueschist is a rock — a mix of grains or minerals; Glaucophane is a single mineral. Blueschist is the rock; glaucophane is the blue mineral in it.
Could you tell them apart from a blurry close-up?
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