Mudrock
Mudrock is a fine-grained sedimentary rock composed mainly of clay- and silt-sized particles. Mudstone, shale, and siltstone are common types.
Clay mineral: A fine-grained hydrous mineral, typically a phyllosilicate, that forms through weathering or alteration. Clay minerals make up much of mudrock’s finest fraction and strongly affect its behavior.
Sedimentation: The settling and accumulation of particles from water, air, or other transporting media. Mudrock begins when fine particles settle and accumulate in a depositional environment.
Shale: A fine-grained sedimentary rock that splits readily along thin, roughly parallel layers. Shale is a fissile mudrock, distinguished by its tendency to split into sheets.
Shale gas: Natural gas produced from organic-rich shale and other fine-grained, low-permeability rocks. Some mudrocks contain gas that requires hydraulic fracturing or other stimulation to produce.
Silt: Sediment composed of particles finer than sand and coarser than clay. Silt-sized grains distinguish many mudrocks from rocks dominated by clay.
Flocculation: The aggregation of fine particles into larger clusters, often promoted by changes in water chemistry. Clay particles can settle faster after flocculating in saline water.
Mudstone: A fine-grained sedimentary rock composed mainly of mud-sized particles that does not split readily into thin sheets. Mudstone is a non-fissile mudrock, unlike shale.
Source rock: An organic-rich rock capable of generating petroleum when buried and heated. Organic-rich mudrock commonly generates oil and gas during burial.
Wentworth scale: A grain-size classification system for sediment, ranging from clay to boulders. Its size boundaries define the clay and silt fractions in mudrock.
Compaction (geology): The reduction of sediment volume as overburden pressure rearranges grains and expels pore fluid. Compaction reduces pore space as buried mud becomes mudrock.