metamorphic
Blue-gray limestone or marble fragment
Calcite-rich carbonate rock; likely calcitic marble (CaCO₃), though limestone is possible
AI-generated identification · may be incorrectPale blue-gray, dull to slightly vitreous, with a granular crystalline texture and irregular fracture; calcite has Mohs hardness 3, rhombohedral cleavage, and specific gravity about 2.7. The rough surface and apparent pale veining are consistent with a carbonate stone.
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Physical properties
Pale blue-gray, dull to slightly vitreous, with a granular crystalline texture and irregular fracture; calcite has Mohs hardness 3, rhombohedral cleavage, and specific gravity about 2.7. The rough surface and apparent pale veining are consistent with a carbonate stone.
Formation & geological history
Marble forms when limestone recrystallizes under heat and pressure during regional or contact metamorphism; limestone forms by marine carbonate deposition. Carbonate rocks range from Precambrian to modern geological ages, so age cannot be determined from the image.
Uses & applications
Used for countertops, tile, sculpture, aggregate, and architectural facing; attractive polished pieces may be decorative, but this small fragment has minimal commercial value.
Geological facts
Calcite strongly effervesces with dilute hydrochloric acid; marble may react less readily if coarse-grained. Blue-gray coloration can result from graphite, organic matter, or minor silicate minerals.
Field identification & locations
Test an inconspicuous spot with vinegar or dilute acid, inspect for calcite cleavage, and compare with a steel knife: calcite scratches easily. Common sources include metamorphic belts and carbonate quarries worldwide.
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