metamorphic
Slate
Foliated Metamorphic Rock (primarily composed of quartz, illite, and chlorite)
Hardness: 2.5–4.0 Mohs; Color: Grey, black, green, or rusty brown; Luster: Dull to satin; Structure: Foliated with slaty cleavage; SG: 2.7–2.8
- Hardness
- 2
- Color
- Grey, black, green, or rusty brown
- Luster
- Dull to satin
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Physical properties
Hardness: 2.5–4.0 Mohs; Color: Grey, black, green, or rusty brown; Luster: Dull to satin; Structure: Foliated with slaty cleavage; SG: 2.7–2.8
Formation & geological history
Formed from the low-grade metamorphism of shale or mudstone under relatively low pressure and temperature conditions. It typically occurs in regions of regional metamorphism where tectonic plates converge.
Uses & applications
Extensively used in construction for roofing tiles, flooring, paving stones, and laboratory tabletops due to its durability and low water absorption.
Geological facts
Slate is famous for its 'slaty cleavage,' allowing it to be split into thin, flat sheets. Historically, it was widely used as writing boards (blackboards and handheld slates) in schools.
Field identification & locations
Identify in the field by its fine-grained texture and ability to split into thin, flat plates. It is commonly found in mountainous regions such as the Appalachian Mountains in the US or North Wales in the UK.
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