sedimentary
Shale (Beach-worn)
Laminated Pelite (primarily clay minerals and quartz)
Hardness: 3-4 (Mohs); Color: Dark grey to charcoal; Luster: Dull/Earthy; Structure: Fine-grained, fissile (layers visible on the edges); Cleavage: Perfect basal-like cleavage along bedding planes.
- Hardness
- 3-4 (Mohs)
- Color
- Dark grey to charcoal
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3-4 (Mohs); Color: Dark grey to charcoal; Luster: Dull/Earthy; Structure: Fine-grained, fissile (layers visible on the edges); Cleavage: Perfect basal-like cleavage along bedding planes.
Formation & geological history
Formed through the lithification of mud and clay in low-energy environments like lake beds or deep ocean basins. This specimen shows significant rounding and frosting from wave action on a beach.
Uses & applications
Used industrially as a source of clay for ceramics, cement production, and as a precursor for some petroleum products. Not used in jewelry.
Geological facts
Shale is the most common sedimentary rock on Earth, making up an estimated 70% of the sedimentary crust. It is often the primary source rock for oil and natural gas.
Field identification & locations
Identify in the field by its tendency to break into thin, flat plates (fissility) and its soft, clay-like feel when scratched. Most commonly found in coastal areas where coastal cliffs erode into the surf.
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