metamorphic
Greenstone (likely metamorphosed mafic rock)
Probable chlorite–actinolite–epidote-rich metabasalt; exact identification requires testing
AI-generated identification · may be incorrectCoarse, angular dark green-gray blocks with pale veins, likely quartz or calcite. The fine-grained rock is probably hard (about Mohs 5–7), with a dull to weakly waxy luster; mineral grains and cleavage are not clear enough to confirm from the image.
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Physical properties
Coarse, angular dark green-gray blocks with pale veins, likely quartz or calcite. The fine-grained rock is probably hard (about Mohs 5–7), with a dull to weakly waxy luster; mineral grains and cleavage are not clear enough to confirm from the image.
Formation & geological history
Greenstone forms when basalt or related mafic rock is altered by low-grade metamorphism and fluid circulation. The white veins formed later as minerals filled fractures; a precise age cannot be determined from the photograph.
Uses & applications
Used locally as building or paving stone and sometimes as decorative aggregate; attractive, sound pieces may be cut or polished for ornaments.
Geological facts
The name “greenstone” describes color and alteration, not a single mineral or uniquely defined rock type.
Field identification & locations
The green-gray color and white cross-cutting vein favor altered mafic rock. Near 12.6°S, 38.1°W in Bahia, such rocks are plausible, but the image alone cannot establish the source; a fresh surface, hardness, and acid tests would help distinguish quartz from calcite veins.
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