Slate

Physical Properties

Hardness: 2.5-4 (Mohs); Color: Dark grey to charcoal; Luster: Dull/Matte; Structure: Very fine-grained with slaty cleavage; Cleavage: Perfect planar; Specific Gravity: 2.7-2.8

Formation & Geological History

Formed from the low-grade metamorphism of shale or mudstone under relatively low pressure and temperature conditions, typically associated with regional metamorphism in fold belts.

Uses & Applications

Used for roofing tiles, flooring, laboratory tabletops, electrical panels, and school chalkboards. Also popular in landscaping and as a substrate for reptile enclosures.

Geological Facts

Slate is unique because it can be split into very thin, durable sheets due to its foliation. Before the invention of modern paper, students used small slabs of slate as writing surfaces.

Field Identification & Locations

Identify in the field by its tendency to break into flat, smooth slabs. It is commonly found in mountainous regions such as the Appalachian Mountains in the US, Wales in the UK, and Brazil.

Identified on: 5/9/2026

Mode: Standard