sedimentary
Dark shale or mudstone
Fine-grained siliciclastic sedimentary rock, chiefly clay minerals and quartz
AI-generated identification · may be incorrectDark gray to black, dull to slightly satiny, with very fine grains and irregular, thin layering or fissility. Typical hardness is about 2–4 Mohs; mineral grains and crystal structure are not distinguishable in the image.
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Physical properties
Dark gray to black, dull to slightly satiny, with very fine grains and irregular, thin layering or fissility. Typical hardness is about 2–4 Mohs; mineral grains and crystal structure are not distinguishable in the image.
Formation & geological history
Formed by compaction and cementation of clay- and silt-sized sediment, often in quiet-water settings such as lake or seafloor mud. Its age cannot be determined from appearance alone.
Uses & applications
Shale and mudstone are used as raw materials for cement and brick; some varieties are important petroleum source rocks. This small specimen is chiefly suitable for study or collecting.
Geological facts
Shale splits along bedding more readily than massive mudstone; weathering and handling can make its layered surfaces appear irregular.
Field identification & locations
Look for extremely fine texture, dark color, and flat or flaky breaks; compare with slate, which is harder and splits into smoother, more uniform sheets. Dark shales occur in sedimentary basins worldwide.
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