Slate

Physical Properties

Hardness: 2.5-4 (Mohs); Color: Dark grey, bluish-grey, or black; Luster: Dull to satiny; Structure: Very fine-grained with distinct slaty cleavage; Gravity: 2.7-2.9

Formation & Geological History

Formed through low-grade regional metamorphism of shale or mudstone under relatively low pressure and temperature conditions. It develops distinct layers due to the alignment of clay minerals.

Uses & Applications

Used widely in construction for roofing shingles, floor tiles, and billiard table tops due to its durability and ability to split into thin sheets.

Geological Facts

Slate has been used for hundreds of years as blackboards and handheld writing tablets before paper became cheap and common. It is exceptionally waterproof and fire-resistant.

Field Identification & Locations

Identify by its ability to split into thin, flat layers (slaty cleavage) and the dull 'clink' sound it makes when struck. Often found in mountainous regions or areas of tectonic activity.

Identified on: 4/15/2026

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