igneous
Iron-stained quartz-rich rock, possibly weathered granite or pegmatite
Quartz (SiO₂) with probable feldspar and iron-oxide staining; exact identification is uncertain from the photograph
AI-generated identification · may be incorrectTan to yellow-brown, irregular and granular, with a dull to locally glassy luster. Quartz hardness is 7 Mohs; feldspar is about 6, and reddish-brown areas are likely iron oxides. Crystal faces and cleavage are not sufficiently clear for confident species identification.
Identified More igneous →
Explore Iron-stained quartz-rich rock, possibly weathered granite or pegmatite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Tan to yellow-brown, irregular and granular, with a dull to locally glassy luster. Quartz hardness is 7 Mohs; feldspar is about 6, and reddish-brown areas are likely iron oxides. Crystal faces and cleavage are not sufficiently clear for confident species identification.
Formation & geological history
Likely an altered or weathered felsic igneous fragment, formed from silica-rich magma and later stained by oxidation of iron-bearing minerals. Such rocks are commonly Precambrian in the Duluth, Minnesota–northeastern Minnesota region, although the specimen’s age cannot be determined visually.
Uses & applications
Primarily a geological or hobby specimen; quartz-rich material may be used as aggregate or silica feedstock, but this small piece has no commercial value.
Geological facts
The yellow-brown coloration is commonly produced by limonite/goethite coatings or alteration. A white streak and strong glass-scratching ability would support quartz, while abundant flat cleavage surfaces would suggest feldspar.
Field identification & locations
Commonly found in glacial sediments and weathered outcrops near 46.7°N, 92.0°W. Test with a steel knife, inspect fresh broken surfaces, and use a hand lens; acid testing is unnecessary. A clearer photo against a plain background would improve identification.
