sedimentary
Shale with Iron Oxide Staining
Fissile Mudstone (primarily clay minerals and quartz)
Hardness: 3-4 (Mohs scale), Color: Gray to black with yellow/red/brown iron staining, Luster: Dull or earthy, Crystal structure: Microcrystalline (not visible), Cleavage: Fissile (splits into thin layers)
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Physical properties
Hardness: 3-4 (Mohs scale), Color: Gray to black with yellow/red/brown iron staining, Luster: Dull or earthy, Crystal structure: Microcrystalline (not visible), Cleavage: Fissile (splits into thin layers)
Formation & geological history
Formed through the compaction of silt and clay-sized mineral particles over millions of years, typically in slow-moving water environments like lake beds or deep ocean floors.
Uses & applications
Used in the production of clay for bricks, cement, and as a source for natural gas (shale gas). Higher quality pieces may contain fossils.
Geological facts
Shale is the most common sedimentary rock on Earth. It often contains iron sulfides like pyrite, which can weather into the yellow/orange iron oxides visible on this specimen's surface.
Field identification & locations
Identify in the field by its tendency to split into flat, thin sheets (fissility). It feels smoother than sandstone but grittier than claystone. Common in basin regions worldwide.
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