Greenschist

Physical Properties

Hardness: 3.5 to 4.5. Color: Distinctive pale to dark green. Luster: Dull to pearly. Crystal Structure: Fine-grained with a foliated (schistose) texture. Cleavage: Good in one direction due to mica-like minerals. Specific Gravity: 2.8-3.0.

Formation & Geological History

Formed through regional metamorphism of mafic igneous rocks (like basalt) or sediment at low temperatures and high pressures. This process occurs along convergent plate boundaries and typically dates from various eras, including the Paleozoic.

Uses & Applications

Commonly used as decorative stone, crushed stone for road construction, and occasionally in sculptures. Historically used for architectural facades and garden paths.

Geological Facts

The 'green' in greenschist comes primarily from the mineral chlorite. It represents the 'greenschist facies' in metamorphic petrology, a specific range of temperature and pressure conditions (approx. 300 to 450 degrees Celsius).

Field Identification & Locations

Identify in the field by its green hue, ability to be scratched by a steel blade, and its 'slaty' or layered appearance. Found in mountain ranges such as the Appalachians and the Alps. Essential for mapping ancient tectonic subduction zones.

Identified on: 4/14/2026

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