metamorphic
Pegmatitic gneiss with a quartz–feldspar vein
Quartz–feldspar-rich gneiss, locally cut by a granitic pegmatite vein
AI-generated identification · may be incorrectCoarse, mottled gray-and-pink rock with a dark, foliated or banded matrix and a pale salmon-colored quartz–feldspar mass. Quartz has Mohs hardness 7; feldspar 6; mica and other dark minerals are typically softer. The minerals are crystalline and mostly show poor cleavage as a rock aggregate.
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Physical properties
Coarse, mottled gray-and-pink rock with a dark, foliated or banded matrix and a pale salmon-colored quartz–feldspar mass. Quartz has Mohs hardness 7; feldspar 6; mica and other dark minerals are typically softer. The minerals are crystalline and mostly show poor cleavage as a rock aggregate.
Formation & geological history
Likely formed when a granitic parent rock was metamorphosed under heat and pressure, developing gneissic banding; silica- and feldspar-rich melt or fluids later crystallized in a coarse vein. Such rocks form in ancient continental crust, but the specimen’s age and locality cannot be determined from the image.
Uses & applications
Gneiss is used as dimension stone, paving, and aggregate; pegmatite may supply feldspar, quartz, and mica. This rounded specimen is mainly suitable for collecting or display.
Geological facts
The pink area is consistent with potassium feldspar, while the light gray material may include quartz and feldspar; the dark matrix likely contains biotite or amphibole.
Field identification & locations
Look for coarse interlocking crystals, contrasting light and dark mineral bands, and a coarse pink-white vein. Similar rocks occur in metamorphic terranes worldwide; the exact identification would benefit from a fresh surface and locality information.
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