igneous
Speckled granite or granitic gneiss pebble
Granite; chiefly quartz, feldspar, and biotite/hornblende
AI-generated identification · may be incorrectMedium- to coarse-grained, black-and-white “salt-and-pepper” texture with interlocking crystals; typically Mohs 6–7, vitreous to dull luster, no obvious cleavage as a whole, and specific gravity about 2.6–2.8. The rounded shape indicates water or abrasion wear.
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Physical properties
Medium- to coarse-grained, black-and-white “salt-and-pepper” texture with interlocking crystals; typically Mohs 6–7, vitreous to dull luster, no obvious cleavage as a whole, and specific gravity about 2.6–2.8. The rounded shape indicates water or abrasion wear.
Formation & geological history
Likely an eroded granitoid pebble formed by slow crystallization of silica-rich magma deep in Earth’s crust, generally Precambrian to Mesozoic in age; the image cannot distinguish granite from closely related gneiss or diorite.
Uses & applications
Commonly used as aggregate, paving stone, monuments, countertops, and landscaping material; this small rounded specimen has little commercial value.
Geological facts
The pale grains are commonly quartz and plagioclase/alkali feldspar, while dark grains are biotite or amphibole. Near 23.7°N, 99.2°W, such pebbles are plausible as transported material from nearby crystalline highlands, though the exact source cannot be determined visually.
Field identification & locations
Identify it by the visible interlocking black, white, and gray grains and by its inability to scratch easily with a steel knife. A vinegar test should show no fizz; a streak test is generally white and uninformative.
