metamorphic
Purple Slate
Foliated slate (Pelitic origin)
Hardness: 2.5-4 Mohs; color: purple to maroon with gray or brown weathering; luster: dull to slightly silky; structure: fine-grained, foliated with distinct slaty cleavage; cleavage: excellent planar cleavage.
- Hardness
- 2
- Color
- purple to maroon with gray or brown weathering
- Luster
- dull to slightly silky
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Physical properties
Hardness: 2.5-4 Mohs; color: purple to maroon with gray or brown weathering; luster: dull to slightly silky; structure: fine-grained, foliated with distinct slaty cleavage; cleavage: excellent planar cleavage.
Formation & geological history
Formed through the low-grade regional metamorphism of shale or mudstone. The purple color is typically caused by the oxidation of iron (hematite) within the sediment layers before metamorphism. Often dates back to the Paleozoic era.
Uses & applications
Commonly used for roofing tiles, billiard table tops, chalkboard surfaces, flooring, and decorative garden landscaping stones.
Geological facts
The distinct purple hue is highly prized for architectural aesthetics. Unlike many other rocks, slate can be split into very thin, durable sheets due to the alignment of its microscopic mica minerals.
Field identification & locations
Identify in the field by its ability to split into flat, thin plates and its 'clinking' sound when struck compared to the 'thud' of shale. Commonly found in folded mountain belts like the Appalachian Mountains (Vermont/New York) or Wales.
