igneous
Weathered feldspar-rich granite or granitic pegmatite
Altered granite/pegmatite, composed mainly of quartz (SiO₂), alkali feldspar, plagioclase, and dark mica or amphibole
AI-generated identification · may be incorrectCoarse, visibly interlocking crystals with cream to pink feldspar, translucent gray quartz, and dark altered minerals; vitreous to dull luster, irregular fracture, no obvious cleavage in the whole specimen. Typical hardness is about 6–7 Mohs and specific gravity roughly 2.6–2.7.
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Physical properties
Coarse, visibly interlocking crystals with cream to pink feldspar, translucent gray quartz, and dark altered minerals; vitreous to dull luster, irregular fracture, no obvious cleavage in the whole specimen. Typical hardness is about 6–7 Mohs and specific gravity roughly 2.6–2.7.
Formation & geological history
Slow cooling of silica-rich magma produced the coarse crystalline texture, likely millions to billions of years ago; later weathering or hydrothermal alteration caused the brown staining and softened surfaces.
Uses & applications
Granite is widely used as dimension stone, countertops, aggregate, and monuments; attractive pegmatitic pieces are collected but are generally not jewelry-grade.
Geological facts
The rusty brown colors are commonly iron-oxide weathering products, while pale granular zones are feldspar and quartz. A glassy quartz grain should scratch ordinary glass, whereas feldspar generally does not.
Field identification & locations
Common in continental crust, mountain belts, and pegmatite districts worldwide. Identify it by its coarse interlocking quartz–feldspar texture and lack of layering or foliation; a hand lens helps distinguish quartz from feldspar.
