igneous
Granitic Pebble with Mafic Inclusion
Granite pebble with biotite/hornblende clot (xenolith/enclave)
AI-generated identification · may be incorrectHardness 6 to 7 on Mohs scale; mottled whitish, pinkish-buff, and gray with a distinct dark gray-black spot; dull to vitreous luster; phaneritic/granular texture, visibly rounded and smoothed by water erosion; specific gravity approximately 2.6 - 2.7.
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Physical properties
Hardness 6 to 7 on Mohs scale; mottled whitish, pinkish-buff, and gray with a distinct dark gray-black spot; dull to vitreous luster; phaneritic/granular texture, visibly rounded and smoothed by water erosion; specific gravity approximately 2.6 - 2.7.
Formation & geological history
Formed deep underground from the slow crystallization of felsic magma, creating an interlocking mixture of quartz and feldspars. The dark spot is a concentration of mafic minerals (such as biotite mica or amphibole/hornblende). Later exposed, weathered, transported, and water-worn into a stream or beach pebble.
Uses & applications
Common river gravel used in landscaping, road construction aggregate, or polished by hobbyist rock tumblers.
Geological facts
Dark clusters or spots within granite are often referred to by geologists as enclaves or 'restite'—leftover refractory minerals from the deep crustal source rock that melted to form the granite.
Field identification & locations
Found widely across riverbeds, beaches, and glacial deposits worldwide. Identifiable by its rounded form, visible quartz and feldspar grain boundaries, and high scratch resistance against a steel knife.
