metamorphic
Glaucophane Schist (Blueschist)
Blueschist (Glaucophane-bearing schist)
Hardness: 5-6 (Mohs scale); Color: Blue to lavender, blue-grey; Luster: Pearly to vitreous or silky; Crystal structure: Monoclinic (prismatic); Cleavage: Perfect in two directions; Specific gravity: 3.0-3.3
- Hardness
- 5-6 (Mohs scale)
- Color
- Blue to lavender, blue-grey
- Luster
- Pearly to vitreous or silky
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Blue to lavender, blue-grey; Luster: Pearly to vitreous or silky; Crystal structure: Monoclinic (prismatic); Cleavage: Perfect in two directions; Specific gravity: 3.0-3.3
Formation & geological history
Formed through high-pressure, low-temperature metamorphism (subduction zone metamorphism). Usually found in mountain belts where oceanic crust was forced beneath continental crust.
Uses & applications
Primarily used for geological research and as an indicator of ancient tectonic subduction zones; occasionally used as decorative landscaping stone or for minor lapidary work.
Geological facts
Blueschist is often called 'high-pressure' rock because it requires pressures of several kilobars but temperatures below 500 degrees Celsius to form, representing a specific metamorphic facies.
Field identification & locations
Identify by its distinct blue-to-grey color and foliated (layered) texture. Commonly found in coastal ranges like California (Franciscan Complex) or the Alps. Look for needle-like crystals of blue glaucophane.
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