metamorphic

Quartz-bearing dark rock, possibly hornfels or basalt

Probable quartz–feldspar rock; exact identification requires testing

AI-generated identification · may be incorrect

Dark gray-brown, dull to weakly crystalline matrix with a prominent cream-white mineral patch, likely quartz or feldspar. Estimated hardness 5–7 Mohs; cleavage and specific gravity cannot be determined reliably from the image.

Identified September 19, 2026More metamorphic →

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Physical properties

Formation & geological history

Could represent a metamorphosed fine-grained volcanic or sedimentary rock, or less likely altered basalt; formation age and locality are indeterminate from appearance alone.

Uses & applications

Typically a field specimen or curiosity; similar rocks may be used as aggregate, roadstone, or decorative stone, but this small piece has no practical industrial value.

Geological facts

The pale patch may be quartz, feldspar, calcite, or weathered alteration material. A glassy luster, conchoidal fracture, and no reaction to dilute acid would favor quartz; fizzing would suggest calcite.

Field identification & locations

Inspect fresh surfaces, test hardness against steel and glass, examine grain size with a loupe, and apply dilute hydrochloric acid only with care. Exact classification requires a clean break or thin section.