metamorphic

Polished black slate or schist slab

Slate/schist, composed mainly of fine-grained mica, quartz, and chlorite

AI-generated identification · may be incorrect

Dark gray-black, finely foliated, with a silky to dull luster and thin rusty-orange mineral veins, likely iron-oxide-stained quartz or calcite. Typical hardness is about 3–6 Mohs depending on composition; strong planar cleavage may produce flat splits.

Identified September 22, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or mudstone underwent low- to medium-grade metamorphism, generally during Paleozoic or older mountain-building events. The polished surface appears human-finished, obscuring much of the natural texture.

Uses & applications

Used for roofing, flooring, wall cladding, countertops, landscaping, and decorative slabs; attractive pieces may be sold as architectural stone rather than specimens.

Geological facts

The orange lines likely represent oxidized iron minerals along fractures or veins, commonly limonite/goethite. Slate has very fine foliation, whereas schist normally shows more visible mica flakes.

Field identification & locations

Identify by its dark color, planar foliation, relatively low porosity, and tendency to split along layers; a knife may scratch softer slate but not harder schist. Common sources include Wales, Vermont, Spain, Brazil, and India.