Greenschist

Physical Properties

Hardness: 3.5-4.5 on Mohs scale; Color: Sage green, grey-green, or olive; Luster: Pearly to dull; Crystal structure: Monoclinic (foliated); Cleavage: Perfect in one direction; Specific gravity: 2.6–3.3

Formation & Geological History

Formed through regional metamorphism of mafic igneous rocks (like basalt or gabbro) or sedimentary rocks under low-temperature and medium-pressure conditions, typically in subduction zones or orogenic belts.

Uses & Applications

Used primarily in construction for building stone, decorative landscaping, and architectural facades; historically used as a source for copper or iron if associated with ore deposits.

Geological Facts

The 'green' in greenschist comes from minerals like chlorite, epidote, and actinolite. It represents a specific 'metamorphic facies' which helps geologists map the pressure and temperature history of an entire mountain range.

Field Identification & Locations

Identify in the field by its distinct green hue and foliated (layered) texture that allows it to split into thin sheets. Commonly found in old mountain chains like the Appalachians or the Alps. Look for its characteristic soapy or greasy feel when chlorite is dominant.

Identified on: 5/4/2026

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