metamorphic
Banded Slate (Lithified Mudstone)
Low-grade Metamorphosed Mudstone / Slate
Hardness: 2.5-4 (Mohs); Color: Dark grey, charcoal to black with pale grey or tan bands; Luster: Dull to slightly waxy; Structure: Foliated with fine-grained slaty cleavage; Gravity: 2.7-2.8
- Hardness
- 2
- Color
- Dark grey, charcoal to black with pale grey or tan bands
- Luster
- Dull to slightly waxy
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Physical properties
Hardness: 2.5-4 (Mohs); Color: Dark grey, charcoal to black with pale grey or tan bands; Luster: Dull to slightly waxy; Structure: Foliated with fine-grained slaty cleavage; Gravity: 2.7-2.8
Formation & geological history
Formed from the regional metamorphism of clay-rich sedimentary mudstone or siltstone. These rocks are typically Proterozoic to Paleozoic in age, formed under low pressure and temperature conditions that preserve original bedding layers.
Uses & applications
Commonly used in construction as roofing tiles, flooring, and blackboards. Water-smoothed specimens like this are often used in landscaping, decorative pebbles, or as 'worry stones' for collectors.
Geological facts
The distinct bands in these pebbles represent original sedimentary layering (varves) from the time the silt was deposited, which survived the metamorphosis into stone. High-quality slate is famous for its 'fissility,' allowing it to be split into thin, flat sheets.
Field identification & locations
Identify in the field by its fine-grained texture, dark color, and characteristic parallel banding. Often found in riverbeds or coastal areas near ancient mountain ranges. It will feel smoother than sandstone but grittier than obsidian.
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