metamorphic
Glaucophane Schist
Glaucophane-bearing Schist (Na2(Mg,Fe)3Al2Si8O22(OH)2)
Hardness: 5-6 (Mohs scale); Color: Blue-grey, bluish-green, to dark blue; Luster: Pearly to silky; Crystal structure: Monoclinic; Schistose texture with visible foliation.
- Hardness
- 5-6 (Mohs scale)
- Color
- Blue-grey, bluish-green, to dark blue
- Luster
- Pearly to silky
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Blue-grey, bluish-green, to dark blue; Luster: Pearly to silky; Crystal structure: Monoclinic; Schistose texture with visible foliation.
Formation & geological history
Formed through high-pressure, low-temperature metamorphism, typically occurring in subduction zones where oceanic crust is pushed beneath continental crust. These are often referred to as Blueschist facies rocks.
Uses & applications
Primarily of interest to geologists and mineral collectors as indicators of tectonic plate boundaries; occasionally used as decorative stone or in landscaping.
Geological facts
Glaucophane is significant because it indicates the rock reached extreme pressures deep within the Earth without being exposed to high temperatures, typically at depths of 15 to 30 kilometers.
Field identification & locations
Identify by its distinctive bluish color and foliated (layered) texture. High concentration in tectonic zones like the California Coast Ranges, the Alps, and Japan.
