metamorphic

Slate

Slate; fine-grained metamorphosed shale, commonly quartz–muscovite/chlorite rich

AI-generated identification · may be incorrect

Typically gray to blue-gray, very fine-grained, dull to silky luster, with strong slaty cleavage that allows splitting into thin sheets; hardness about 3–4 Mohs and specific gravity roughly 2.7–2.8. The visible rusty yellow-brown streaks are likely iron-oxide weathering, while pale veins may contain quartz or calcite.

Identified September 14, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or mudstone underwent low-grade regional metamorphism, commonly during mountain building; its exact geological age depends on the outcrop and cannot be determined from the image. The layered, fissile texture is characteristic of aligned clay minerals recrystallizing under pressure.

Uses & applications

Used for roofing, floor and wall tiles, paving, steps, gravestones, billiard tables, and landscaping; attractive specimens may be collected, though this appears to be ordinary building or outcrop material.

Geological facts

Slate is distinguished from shale by metamorphic cleavage: it breaks along planar surfaces rather than merely following original sedimentary bedding. It commonly grades into phyllite as metamorphic intensity increases.

Field identification & locations

Identify it by its fine grain, gray color, planar cleavage, and ability to split into durable flat sheets; common in metamorphic belts worldwide, including Wales, Vermont, Spain, Brazil, and China. Value is typically $5–$30 for common hand specimens, or about $20–$100+ for attractive collector pieces.