igneous
Quartz-rich rock, likely milky quartz with dark mica/amphibole
Quartz (SiO₂) in a granitic or metamorphic matrix; dark portion may be biotite or amphibole
AI-generated identification · may be incorrectSmall rounded fragment with translucent white-gray quartz and a contrasting black, sparkly granular zone. Quartz has Mohs hardness 7, vitreous luster, no cleavage, and conchoidal fracture; the dark minerals are softer or similarly hard and may show flaky cleavage. Specific gravity is roughly 2.65–3.1.
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Physical properties
Small rounded fragment with translucent white-gray quartz and a contrasting black, sparkly granular zone. Quartz has Mohs hardness 7, vitreous luster, no cleavage, and conchoidal fracture; the dark minerals are softer or similarly hard and may show flaky cleavage. Specific gravity is roughly 2.65–3.1.
Formation & geological history
Probably derived from granite, gneiss, or a quartz vein, formed when silica-rich magma crystallized or when metamorphic fluids deposited quartz. The specimen itself has no reliable age from the photograph; rocks of this type in the Rochester, New York region commonly relate to Paleozoic bedrock and glacial transport.
Uses & applications
Common quartz-bearing rock is used as aggregate, construction stone, and silica feedstock; attractive pieces are collected but usually have little commercial jewelry value.
Geological facts
The sharp boundary between pale quartz and dark minerals is characteristic of a quartz-rich vein or felsic rock. A steel file should not scratch the quartz; a glass bottle may be scratched by it.
Field identification & locations
Quartz-rich fragments are plausible near 43.1°N, 77.6°W, where glacial deposits contain material transported from surrounding crystalline terrains. Confirm with a hardness test, streak (white), and loupe examination for mica flakes or amphibole prisms.
