sedimentary
Shale (with Iron Oxide staining)
Fissile Mudstone (primarily Quartz and Clay minerals)
Hardness: 3 on Mohs scale; Color: Gray to black with red/brown iron staining; Luster: Dull/Earthy; Structure: Fine-grained, clastic; Cleavage: High fissility (splits into thin layers); Specific Gravity: 2.4-2.8
- Hardness
- 3 on Mohs scale
- Color
- Gray to black with red/brown iron staining
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Gray to black with red/brown iron staining; Luster: Dull/Earthy; Structure: Fine-grained, clastic; Cleavage: High fissility (splits into thin layers); Specific Gravity: 2.4-2.8
Formation & geological history
Formed through the compaction of silt and clay-size mineral particles. These sediments are typically deposited in low-energy environments like lake bottoms, river deltas, or floodplains. Age varies widely from Precambrian to Cenozoic based on location.
Uses & applications
Used as a source of clay for ceramics and bricks, a filler in paints and plastics, and as a raw material in Portland cement. It is also significant in the energy industry as a source rock for natural gas and oil.
Geological facts
Shale is the most common sedimentary rock on Earth, making up approximately 70% of the rocks in the Earth's crust. It often preserves fossils more effectively than coarser-grained sedimentary rocks.
Field identification & locations
Identify in the field by its ability to split into thin, flat plates (fissility) and its soft, fine-textured feel. It is commonly found in sedimentary basins and outcrops near water bodies. Collectors should look for impressions of leaves or small shells within the layers.
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