thumb|right|Mudstone on east beach of [[Lyme Regis, England]]
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from shale by its lack of fissility.
The term mudstone is also used to describe carbonate rocks (limestone or dolomite) that are composed predominantly of carbonate mud. However, in most contexts, the term refers to siliciclastic mudstone, composed mostly of silicate minerals.
Definition
There is not a single definition of mudstone that has gained general acceptance, though there is wide agreement that mudstones are fine-grained sedimentary rocks, composed mostly of silicate grains with a grain size less than . Individual grains this size are too small to be distinguished without a microscope, which means that most classifications emphasize texture rather than mineral composition, and mudstones have historically received less attention from petrologists than have sandstones. The simplest definition is that a mudstone is a fine-grained clastic sedimentary rock that is not laminated or fissile. Another definition is that mudstone is a sedimentary rock in which neither silt, clay, nor coarser grains is predominant. Rock of this composition that does show laminations or fissility is sometimes described as mudshale rather than mudstone.
Carbonate mudstone
thumb|A mudstone: few small components in a micritic matrix, width of picture is 32 mm
In the Dunham classification (Dunham, 1962) system of limestones, a mudstone is defined as a mud-supported carbonate rock that contains less than 10% grains. Most recently, this definition has been clarified as a matrix-supported carbonate-dominated rock composed of more than 90% carbonate mud (<63 μm) component.) to a grain size of less than or equal to 30 μm. Wright (1992) proposed a further increase to the upper limit for the matrix size in order to bring it into line with the upper limit for silt (63 μm).
Mudstone mineralogy on Mars
thumb|[[Timeline of Mars Science Laboratory#2016 events|Curiosity rover - mudstone mineralogy - 2013 to 2016 on Mars (CheMin; December 13, 2016)<br /><small>NOTE: JK for "John Klein", CB for "Cumberland". CH for "Confidence Hills", MJ for "Mojave", TP for "Telegraph Peak", BK for "Buckskin", OD for "Oudam", MB for "Marimba", QL for "Quela", and SB for Sebina. (For locations/drillings, see image)</small>]]
On December 13, 2016, NASA reported further evidence supporting habitability on the planet Mars as the Curiosity rover climbed higher, studying younger layers, on Mount Sharp. Also reported, the very soluble element boron was detected for the first time on Mars.
See also
- Mudstone on planet Mars
- Aeolis quadrangle
- Composition of Mars
- Timeline of Mars Science Laboratory