Mudstone

[2] The NASA Curiosity rover has found deposits of mudstone on Mars that contain organic substances such as propane, benzene and toluene.

[6] Individual grains this size are too small to be distinguished without a microscope, which means that most classifications emphasize texture rather than mineral composition,[5] and mudstones have historically received less attention from petrologists than have sandstones.

Most recently, this definition has been clarified as a matrix-supported carbonate-dominated rock composed of more than 90% carbonate mud (<63 μm) component.

Wright (1992[13]) 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).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.

[15] In June 2018, NASA reported that Curiosity had detected kerogen and other complex organic compounds from mudstone rocks approximately 3.5 billion years old.