metamorphic
Greenstone Pebble
Metabasalt / Greenstone
Hardness of 5 to 6 on the Mohs scale, typically mottled green, gray-green, or dark green in color due to chlorite, epidote, and actinolite minerals. Luster is dull to sub-vitreous. Massive or fine-grained crystal structure with no distinct cleavage.
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Physical properties
Hardness of 5 to 6 on the Mohs scale, typically mottled green, gray-green, or dark green in color due to chlorite, epidote, and actinolite minerals. Luster is dull to sub-vitreous. Massive or fine-grained crystal structure with no distinct cleavage.
Formation & geological history
Formed by the low-grade metamorphism of mafic igneous rocks (such as basalt or gabbro) under elevated pressure and temperature, commonly occurring in ancient ocean crusts or subduction zone environments.
Uses & applications
Often collected as a beach pebble, used in lapidary work, decorative landscaping, or as a regional lapidary gemstone (such as New Zealand Greenstone or jade substitutes).
Geological facts
The characteristic green color comes from secondary minerals like chlorite, epidote, and actinolite that replace the original pyroxenes and plagioclase during hydrothermal alteration and metamorphism.
Field identification & locations
Easily identified by its smooth, water-worn texture on beaches and its distinct mottled green coloration. Common in glacial tills, riverbeds, and coastal beaches worldwide, particularly in ancient orogenic belts.
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