Mudstone

Mudstone is a fine-grained sedimentary rock composed chiefly of clay- and silt-sized particles. Unlike shale, it lacks pronounced layering that allows it to split into thin sheets.

Mud: A mixture of water and fine mineral particles, chiefly clay and silt. Mudstone forms when mud is buried, compacted, and cemented into rock.
Suspension settling: The sinking of particles suspended in a fluid when turbulence can no longer keep them aloft. Fine particles settle from calm water to build muddy sediment.
Shale: A fine-grained sedimentary rock that splits readily along closely spaced layers. Shale is fissile, whereas mudstone generally lacks easy splitting into thin sheets.
Source rock: A rock containing organic matter that can generate petroleum or natural gas during burial and heating. Organic-rich mudstone can generate hydrocarbons that migrate into reservoirs.
Burgess Shale: A Middle Cambrian fossil deposit in British Columbia, famous for exceptional preservation of soft-bodied organisms. Its fossil-bearing strata include fine-grained mudstones that preserved delicate organisms.
Clay mineral: A group of fine-grained hydrous aluminosilicate minerals with layered crystal structures. Clay minerals commonly make up much of mudstone’s finest fraction.
Flocculation: The aggregation of fine suspended particles into larger clusters. Flocs can help clay particles settle from water more rapidly.
Siltstone: A sedimentary rock composed predominantly of silt-sized grains. Siltstone has a higher proportion of silt-sized particles than typical mudstone.
Caprock: A low-permeability rock layer that impedes the upward movement of fluids or gases. Mudstone can seal reservoirs because its fine pores restrict fluid flow.
Lagerstätte: A fossil deposit with exceptional preservation or unusually abundant fossils. Fine-grained mudstone is a common setting for exceptional fossil preservation.

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