Slate with Iron Staining

Physical Properties

Hardness: 2.5-4; Color: Grey-green base with reddish-brown and orange iron oxide staining; Luster: Dull to pearly; Crystal structure: Microcrystalline (foliated); Cleavage: Perfect slaty cleavage; Specific gravity: 2.7-2.8

Formation & Geological History

Formed through the low-grade regional metamorphism of shale or mudstone under high pressure and low temperature conditions. The iron staining occurs post-metamorphism through the oxidation (weathering) of minerals like pyrite or chlorite.

Uses & Applications

Commonly used for roofing tiles, flooring, garden stones, billiard table tops, and laboratory bench tops due to its durability and cleavage.

Geological Facts

Slate can be split into very thin sheets while maintaining its strength. The colors are caused by trace minerals; iron oxides create reds and yellows, while chlorite creates the green tones seen here.

Field Identification & Locations

Identify in the field by its planar layers (foliation) and the way it rings when lightly struck. It is commonly found in mountainous regions or areas with tectonic history like the Appalachian Mountains or Wales.

Identified on: 5/1/2026

Mode: Standard