Slate

Dark gray, dull to slight sheen, fine-grained, and splits into flat sheets along slaty cleavage. Typical hardness is about 3–4 Mohs; composition and density vary.

Forms when shale or mudstone is weakly metamorphosed under directed pressure, producing aligned microscopic minerals. This process occurred across many geological periods in regional metamorphic belts.

Used for roofing, paving, floor tiles, blackboards, and decorative stone; attractive specimens are collected.

The broad, flat surfaces are characteristic slaty cleavage, not sedimentary bedding. Slate can retain fossils or sedimentary structures if metamorphism was mild.

The image shows a dark, layered slab consistent with slate, though a photo cannot confirm the identification. Look for easy splitting into thin, relatively smooth sheets; slate is common in metamorphic regions worldwide, including Wales and the northeastern United States.