metamorphic
Polished dark breccia or gneiss-like rock
Indeterminate polymictic breccia; likely quartz–feldspar–mica rock with iron-oxide staining
AI-generated identification · may be incorrectDark gray-black, rounded and polished, with irregular pale mineral bands and rusty brown staining. Likely Mohs 6–7, vitreous to dull luster, interlocking granular texture, and no obvious cleavage; exact identification requires hardness, streak, and thin-section tests.
Identified More metamorphic →
Explore Polished dark breccia or gneiss-like rock in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray-black, rounded and polished, with irregular pale mineral bands and rusty brown staining. Likely Mohs 6–7, vitreous to dull luster, interlocking granular texture, and no obvious cleavage; exact identification requires hardness, streak, and thin-section tests.
Formation & geological history
The contrasting fragments or bands suggest brecciation and/or strong metamorphic deformation, later cemented or recrystallized by silica-rich material. Its geological age and locality cannot be determined from the photograph.
Uses & applications
Primarily a decorative or collector specimen; comparable rocks may be used as aggregate, facing stone, or polished ornamental material, but this small piece has little industrial value.
Geological facts
The bright metallic-looking flecks may be pyrite, mica, or iron oxides rather than gold. A polished surface can obscure the original texture and make field identification difficult.
Field identification & locations
Look for a strong reaction to a steel file, glassy quartz grains, and a nonmagnetic or weakly magnetic response; a streak test and acid test can help distinguish minerals. Similar dark breccias and metamorphic rocks occur worldwide.
More like this
