igneous
Pebble with dark mineral inclusion
Likely granitic or gneissic quartz–feldspar pebble with a mafic inclusion; exact identification requires testing
AI-generated identification · may be incorrectRounded, cream-colored fine- to medium-grained stone with a dark gray-black patch, probably biotite-, amphibole-, or magnetite-rich. Likely Mohs hardness 6–7 overall, vitreous to dull luster, massive texture, and no obvious cleavage.
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Physical properties
Rounded, cream-colored fine- to medium-grained stone with a dark gray-black patch, probably biotite-, amphibole-, or magnetite-rich. Likely Mohs hardness 6–7 overall, vitreous to dull luster, massive texture, and no obvious cleavage.
Formation & geological history
Probably an ice- or water-worn glacial/fluvial pebble formed from continental igneous or metamorphic bedrock; its geological age cannot be determined from the image. The dark area may be a mafic xenolith or concentrated ferromagnesian mineral.
Uses & applications
Primarily a natural curiosity, landscaping pebble, or teaching specimen; it has little value for jewelry or construction because of its small size and uncertain identity.
Geological facts
The strong rounding indicates prolonged transport or wave abrasion. A magnet test can detect magnetite, while a fresh scratch test and close-up grain inspection can distinguish granite, gneiss, and other host rocks.
Field identification & locations
Common in glacial deposits, river gravels, beaches, and mixed aggregate worldwide. Typical value is $0–$5; an unusually diagnostic or locality-labeled specimen might sell for $5–$20.
