mudstoneArticle Free Pass mudstone, sedimentary rock composed
primarily of clay- or silt-sized particles (less than 0.063 mm
[0.0025 inch] in diameter); it is not laminated or easily split
into thin layers. Some geologists designate as mudstone any
similar rock that is blocky or massive; others, however, prefer
a broader definition that includes all of the members of the
shale group. See also siltstone. What made you want to look up
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