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Mudrocks are a class of fine grained siliciclastic sedimentary rocks. The varying types of mudrocks include: ''siltstone'', ''claystone'', ''mudstone'', ''slate'', and ''shale''. Most of the particles are less than 0.0625 mm (1/16th mm or 0.0025 inches) and are too small to study readily in the field. At first sight the rock types look quite similar; however, there are important differences in composition and nomenclature. There has been a great deal of disagreement involving the classification of mudrocks. There are a few important hurdles to classification, including: #Mudrocks are the least understood, and one of the most understudied sedimentary rocks to date #It is difficult to study mudrock constituents, due to their diminutive size and susceptibility to weathering on outcrops #And most importantly, there is more than one classification scheme accepted by scientists Mudrocks make up fifty percent of the sedimentary rocks in the geologic record, and are easily the most widespread deposits on Earth. Fine sediment is the most abundant product of erosion, and these sediments contribute to the overall omnipresence of mudrocks. With increased pressure over time the platey clay minerals may become aligned, with the appearance of fissility or parallel layering. This finely bedded material that splits readily into thin layers is called ''shale'', as distinct from ''mudstone''. The lack of fissility or layering in mudstone may be due either to original texture or to the disruption of layering by burrowing organisms in the sediment prior to lithification. From the beginning of civilization, when pottery and mudbricks were made by hand, to now, mudrocks have been important. The first book on mudrocks, ''Geologie des Argils'' by Millot, was not published until 1964; however, scientists, engineers, and oil producers have understood the significance of mudrocks since the discovery of the Burgess Shale and the relatedness of mudrocks and oil. Literature on the elusive yet omnipresent rock-type has been increasing in recent years, and technology continues to allow for better analysis. ==Nomenclature== Mudrocks, by definition, consist of at least fifty percent mud-sized particles. Specifically, mud is composed of silt-sized particles that are between 1/16 – 1/256 of a millimeter in diameter, and clay-sized particles which are less than 1/256 millimeter. Mudrocks contain mostly clay minerals, and quartz and feldspars. They can also contain the following particles at less than 63 micrometres: calcite, dolomite, siderite, pyrite, marcasite, heavy minerals, and even organic carbon.〔 There are various synonyms for fine-grained siliciclastic rocks containing fifty percent or more of its constituents less than 1/256 of a millimeter. Mudstones, shales, lutites, and argillites are common qualifiers, or umbrella-terms; however, the term mudrock has increasingly become the terminology of choice by sedimentary geologists and authors. The term "mudrock" allows for further subdivisions of siltstone, claystone, mudstone, and shale. For example, a siltstone would be made of more than 50-percent grains that equate to 1/16 - 1/256 of a millimeter. "Shale" denotes fissility, which implies an ability to part easily or break parallel to stratification. Siltstone, mudstone, and claystone implies lithified, or hardened, detritus without fissility. Overall, "mudrocks" may be the most useful qualifying term, because it allows for rocks to be divided by its greatest portion of contributing grains and their respective grain size, whether silt, clay, or mud. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「mudrock」の詳細全文を読む スポンサード リンク
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