Glaucophane Schist (Blueschist)

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.

Identified on: 4/16/2026

Mode: Standard