Shale

Shale is a fine-grained sedimentary rock formed from compacted clay- and silt-sized particles. Its fissility allows it to split along thin, closely spaced layers.

Mudrock: Mudrock is a sedimentary rock composed mainly of clay- and silt-sized particles. Shale is a fissile variety within this broader family of fine-grained rocks.
Fissility: Fissility is the tendency of a rock to split into thin sheets along closely spaced, roughly parallel surfaces. This characteristic splitting distinguishes shale from many other mudrocks.
Shale gas: Shale gas is natural gas retained in shale and produced from it through wells. It is one of the most economically significant resources hosted by shale.
Siltstone: Siltstone is a sedimentary rock composed predominantly of silt-sized grains. Unlike typical shale, siltstone is usually non-fissile and dominated by silt.
Clay mineral: Clay minerals are fine-grained phyllosilicates formed by linked sheets of silicon- and oxygen-bearing tetrahedra and aluminum- or magnesium-bearing octahedra. These minerals commonly dominate shale’s fine-grained matrix.
Lamination: Lamination is the arrangement of sedimentary rock into thin, parallel layers formed by changes in deposition or composition. Shale’s fine layers can record changing sediment supply or depositional conditions.
Oil shale: Oil shale is a fine-grained sedimentary rock containing kerogen that can yield liquid hydrocarbons when heated. This shale-like rock is valued for its organic matter rather than conventional oil.
Mudstone: Mudstone is a fine-grained sedimentary rock composed mainly of clay- and silt-sized particles, without pronounced fissility. Its similar composition but weaker tendency to split separates it from shale.
Silt: Silt is sediment whose particles are smaller than sand and larger than clay. Silt-sized grains contribute to shale’s composition alongside clay-sized particles.
Sedimentation: Sedimentation is the deposition and accumulation of particles or precipitated material at Earth’s surface. Shale begins as deposited mud, commonly settling in low-energy water.

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