Greenstone

Physical Properties

Hardness: 3.5 to 5.5 (variable); Color: Dull green to greenish-gray; Luster: Dull or earthy; Crystal structure: Usually fine-grained or massive; Cleavage: Poorly defined or slaty; Specific gravity: 2.8 to 3.0

Formation & Geological History

Formed through the low-grade metamorphism of mafic igneous rocks (such as basalt) under low temperature and pressure conditions (greenschist facies). This specimen shows sign of being a 'beach rock' as it is encrusted with barnacles.

Uses & Applications

Used historically for stone tools and weapons (celt making); currently used as decorative garden stone, crushed stone for construction, or occasionally for carving.

Geological Facts

The green color is primarily due to minerals like chlorite, epidote, and actinolite. The presence of barnacles (Balanomorpha) on its surface indicates this rock spent a significant amount of time in an intertidal or marine environment.

Field Identification & Locations

Identify by its distinctive greenish hue and fine-grained texture. It often feels slightly greasy or soapy if chlorite-rich. Commonly found in ancient volcanic belts and along rocky shorelines where metamorphic bedrock is exposed.

Identified on: 4/23/2026

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