Greenstone

Physical Properties

Hardness: 5-7 (Mohs scale), Color: Dull to dark green, Luster: Dull to waxy, Crystal Structure: Microcrystalline to fine-grained, Cleavage: Generally lacks prominent cleavage in massive form

Formation & Geological History

Formed through the low-grade metamorphism of mafic igneous rocks (like basalt) at low temperatures and pressures. These rocks are often associated with ancient mountain-building events and oceanic crust subduction.

Uses & Applications

Commonly used as crushed stone for road construction and aggregate. High-quality varieties are used for ornamental stones, carvings, and occasionally in jewelry as a substitute for jade.

Geological Facts

The name 'greenstone' refers to various types of green rocks, but in geology, it specifically denotes rocks that have undergone 'greenschist facies' metamorphism, which gives them their characteristic green chlorite minerals.

Field Identification & Locations

Identify by its distinctive dull green color and toughness. It is frequently found in ancient shield regions like the Canadian Shield or the Appalachian Mountains. Use a streak test (usually white/pale green) to differentiate from darker basalt.

Identified on: 4/20/2026

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