igneous
Quartz-rich pegmatite (likely rose/iron-stained quartz)
Quartz, SiO₂, in a coarse granitic pegmatite matrix; possibly with feldspar and mica
AI-generated identification · may be incorrectCoarse, interlocking translucent white to honey-brown crystals with glassy to greasy luster; quartz has Mohs hardness 7, no cleavage, and conchoidal fracture. Brown-red coloration is likely iron-oxide staining; darker gray material may be feldspar or mica.
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Physical properties
Coarse, interlocking translucent white to honey-brown crystals with glassy to greasy luster; quartz has Mohs hardness 7, no cleavage, and conchoidal fracture. Brown-red coloration is likely iron-oxide staining; darker gray material may be feldspar or mica.
Formation & geological history
Likely formed from the late-stage, silica-rich fluids of a granitic intrusion, producing unusually large crystals. The specimen’s exact age cannot be determined from a photograph; pegmatites commonly range from Precambrian to Mesozoic in age.
Uses & applications
Used mainly as a collector specimen or decorative stone; quartz may be valuable for industrial silica, but this rough, mixed specimen is unlikely to have gem value.
Geological facts
The blocky/coarse texture is characteristic of pegmatite rather than ordinary granite. It could also be quartz-bearing hydrothermal rock, but crystal size and texture favor pegmatite.
Field identification & locations
Look for hardness sufficient to scratch glass, lack of reaction to dilute acid, and quartz’s curved fracture. Around 26.7°S, 53.6°W in southern Brazil, granitic and volcanic rocks with quartz-rich veins and pegmatitic material are geologically plausible; a field test is needed to distinguish quartz from feldspar.
