igneous
Quartz-rich breccia or pegmatitic granite fragment
Quartz–feldspar rock; possibly hydrothermal quartz breccia
AI-generated identification · may be incorrectCoarse, angular pale quartz/feldspar fragments in a dark gray matrix, with vitreous to dull luster and no obvious foliation. Estimated hardness is 6–7 for quartz-rich portions; cleavage may occur in feldspar, and density is roughly 2.6–2.8 g/cm³.
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Physical properties
Coarse, angular pale quartz/feldspar fragments in a dark gray matrix, with vitreous to dull luster and no obvious foliation. Estimated hardness is 6–7 for quartz-rich portions; cleavage may occur in feldspar, and density is roughly 2.6–2.8 g/cm³.
Formation & geological history
Likely formed when silica- and feldspar-rich magma crystallized slowly underground, or when fractured rock was cemented by quartz-rich fluids; exact age and process require testing. The rough, broken surface appears natural rather than polished.
Uses & applications
Common material has little commercial value but may be used as aggregate or building stone; attractive quartz-rich pieces can be collected as mineral specimens.
Geological facts
The visible light grains are probably quartz and feldspar, while darker grains may be mica or other mafic minerals. A glassy quartz grain will scratch ordinary glass; feldspar typically shows flat cleavage faces.
Field identification & locations
Look for interlocking crystals, quartz’s lack of cleavage, and feldspar’s two cleavage directions; a hand lens, streak test, hardness test, and acid test would improve identification. Similar rocks occur in granitic and hydrothermal regions worldwide.
