igneous
Pink granite cobble
Granite, typically quartz–alkali feldspar–plagioclase with biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, pink-and-gray, speckled texture with a granular crystalline structure; quartz gives a glassy luster, feldspar is commonly white to salmon-pink, and dark mica or amphibole forms black flecks. Hardness is about 6–7 Mohs; cleavage occurs in feldspar, but granite has no overall cleavage.
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Physical properties
Coarse-grained, pink-and-gray, speckled texture with a granular crystalline structure; quartz gives a glassy luster, feldspar is commonly white to salmon-pink, and dark mica or amphibole forms black flecks. Hardness is about 6–7 Mohs; cleavage occurs in feldspar, but granite has no overall cleavage.
Formation & geological history
An intrusive felsic igneous rock crystallized slowly from silica-rich magma deep in the crust, commonly during Precambrian to younger continental mountain-building events. The rounded form is a naturally weathered and transported cobble.
Uses & applications
Used widely as building stone, paving, aggregate, monuments, countertops, and landscaping rock; attractive pieces may be collected but are generally inexpensive.
Geological facts
The pink color commonly reflects potassium feldspar, while the darker minerals record iron- and magnesium-bearing components. Its granular texture distinguishes it from volcanic rhyolite, which is typically fine-grained.
Field identification & locations
Identify it by visible interlocking crystals of pink feldspar, gray translucent quartz, and black mica/amphibole; a streak test is unhelpful, and acid produces no reaction. Common in continental terrains and glacial or river gravels.
