metamorphic
Polished gray metamorphic pebble, likely marble or quartzite
Uncertain; possibly calcitic marble (CaCO₃) or quartzite (SiO₂) with dark mineral veining
AI-generated identification · may be incorrectSmooth, rounded, light gray to white with dark gray/black patches and possible metallic-looking inclusions; likely vitreous to dull luster. Hardness would be about 3 for marble or 7 for quartzite; no cleavage is visible.
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Physical properties
Smooth, rounded, light gray to white with dark gray/black patches and possible metallic-looking inclusions; likely vitreous to dull luster. Hardness would be about 3 for marble or 7 for quartzite; no cleavage is visible.
Formation & geological history
Likely a naturally water-worn and polished fragment of metamorphic rock formed when limestone or quartz-rich sandstone recrystallized during regional or contact metamorphism. Precise geological age and locality cannot be determined from the image.
Uses & applications
Suitable as a decorative or pocket stone, cabochon, or craft specimen; marble may be used in dimension stone, while quartzite is used for aggregate, paving, and countertops.
Geological facts
The apparent dark areas may be mica, amphibole, graphite, or staining rather than metallic ore. A steel scratch test and dilute hydrochloric-acid test can distinguish quartzite from calcitic marble.
Field identification & locations
Commonly found in stream gravels and metamorphic terrains worldwide, including the Alps, Appalachians, India, Brazil, and Scandinavia. Quartzite resists a steel scratch; marble fizzes with acid and is easily scratched.
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