metamorphic
Slate
Foliated Metamorphic Rock
Hardness: 2.5–4 on Mohs scale; Color: Dark grey to black; Luster: Dull to pearly; Crystal structure: Microcrystalline; Cleavage: Perfect basal cleavage (slaty cleavage); Specific gravity: 2.7–2.8
- Hardness
- 2
- Color
- Dark grey to black
- Luster
- Dull to pearly
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Physical properties
Hardness: 2.5–4 on Mohs scale; Color: Dark grey to black; Luster: Dull to pearly; Crystal structure: Microcrystalline; Cleavage: Perfect basal cleavage (slaty cleavage); Specific gravity: 2.7–2.8
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under low pressure and temperature conditions. It typically dates to various geological eras depending on tectonic activity, often Paleozoic or older.
Uses & applications
Commonly used in roofing tiles, garden landscaping, billiard table tops, blackboards, and interior flooring due to its durability and ability to split into thin sheets.
Geological facts
Slate can be found in a variety of colors besides grey, including purple, green, and cyan, depending on the mineral impurities present like iron and chlorite.
Field identification & locations
Identify in the field by its characteristic flat, planar sheets and the way it rings slightly when struck. It is commonly found in mountainous regions such as North Wales, the Appalachian Mountains, and parts of the Himalayas.
