metamorphic

Slate

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

AI-generated identification · may be incorrect

Dark gray, dull to slightly silky luster, very fine grained, with strong slaty cleavage producing thin planar sheets; hardness about 3–4 Mohs, specific gravity roughly 2.7–2.8. The pale veins are likely quartz or calcite, and rusty patches indicate iron oxidation.

Identified September 18, 2026More metamorphic →

Explore Slate in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Forms when shale or mudstone undergoes low-grade regional metamorphism, typically during mountain building; its precise geological age cannot be determined from the image. Commonly associated with folded and faulted sedimentary sequences.

Uses & applications

Used for roofing, floor and wall tiles, paving, writing slates, and architectural facing; attractive pieces may be collected, though this specimen appears ordinary and unpolished.

Geological facts

Slate preserves original bedding locally but develops a new cleavage from aligned microscopic phyllosilicate minerals. It grades metamorphically toward phyllite with increasing heat and pressure.

Field identification & locations

Identify it by its fine texture, dark color, and ability to split into flat sheets more readily than shale; a streak, hand lens, and acid test can help distinguish quartz/calcite veins. Common in Wales, the northeastern United States, Spain, Brazil, and South Africa.