igneous
Greenstone / altered basalt pebble
Metamorphosed or hydrothermally altered mafic rock; likely chlorite–actinolite basalt (greenstone)
AI-generated identification · may be incorrectFine- to medium-grained, dark green matrix with black and pale mineral grains, weakly subrounded from stream or beach abrasion, and locally glassy/waxy luster. Likely Mohs hardness 5–6; minerals commonly include chlorite, actinolite, epidote, albite, and altered pyroxene;…
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Physical properties
Fine- to medium-grained, dark green matrix with black and pale mineral grains, weakly subrounded from stream or beach abrasion, and locally glassy/waxy luster. Likely Mohs hardness 5–6; minerals commonly include chlorite, actinolite, epidote, albite, and altered pyroxene; cleavage is variable and specific gravity about 2.8–3.2.
Formation & geological history
Originally basalt formed from cooling mafic lava, then altered or weakly metamorphosed by burial, regional metamorphism, or hydrothermal fluids, commonly during Precambrian–Mesozoic tectonic events. The rounded specimen was later transported by water.
Uses & applications
Used locally as durable aggregate, landscaping stone, or decorative pebble; attractive pieces may be collected, but it is generally not a gemstone or high-value ornamental stone.
Geological facts
“Greenstone” is a field term rather than one precise mineral or rock species; its green color typically reflects chlorite, epidote, or actinolite replacing original basalt minerals.
Field identification & locations
Identify it by green color, fine mafic texture, scattered dark grains, and lack of obvious sedimentary layering; a streak, magnetism, acid, and thin-section test would improve identification. Common in ancient volcanic belts, ophiolites, and metamorphic terrains.
