igneous
Greenstone / Basalt
Aphanitic Mafic Igneous Rock (likely altered Basalt)
Hardness: 5-6 (Mohs scale), Color: Dull olive green to dark grey, Luster: Sub-vitreous to dull, Crystal Structure: Microcrystalline (aphanitic), Specific Gravity: 2.8-3.0
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5-6 (Mohs scale), Color: Dull olive green to dark grey, Luster: Sub-vitreous to dull, Crystal Structure: Microcrystalline (aphanitic), Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The greenish tint often suggests low-grade metamorphism or hydrothermal alteration of pyroxene and plagioclase into chlorite or epidote.
Uses & applications
Used primarily as crushed stone for construction, road base, and concrete aggregate. Smooth river-worn specimens are popular in decorative landscaping and as 'worry stones'.
Geological facts
Greenstone belts are some of the oldest known geological formations on Earth, dating back to the Archean Eon. Many such rocks contain significant deposits of gold and copper.
Field identification & locations
Identified in the field by its dark greenish-grey color, density, and lack of visible large crystals (fine-grained). Often found as water-rounded pebbles in riverbeds or coastal areas near volcanic regions.
