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Allochem

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  Allochem   is a term introduced by Folk [1]   to describe the recognisable "grains" in   carbonate rocks . Any fragment from around 0.5 mm upwards in size may be considered an allochem. Examples would include   ooids ,   peloids ,   oncolites ,   pellets ,   fossil   or pre-existing carbonate fragments. Fragments are still termed allochems if they have undergone chemical transformations – for example if an   aragonite   shell were to dissolve and be later replaced by   calcite , the replacement would still be deemed an allochem. [2] Ooids  on the surface of a  limestone ; Carmel Formation (Middle  Jurassic ) of southern Utah, USA. Largest is 1.0 mm in diameter. The allochems are typically embedded in a  matrix  of  micrite  (lime mud) or sparry calcite. This article uses material from the Wikipedia article   Metasyntactic variable , which is released under the  Creative C...
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Arenite

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  Arenite   ( Latin :   Arena , "sand") is a   sedimentary   clastic   rock with sand   grain size   between 0.0625 mm (0.00246 in) and 2 mm (0.08 in) and contain less than 15%   matrix . [1]   The related adjective is   arenaceous . The equivalent   Greek -derived term is   psammite , though this is more commonly used for   metamorphosed   sediments. Arenite Since it refers to grain size rather than chemical composition, the term is used for example in the classification of clastic carbonatic limestones, as the  granulometrically  equivalent term  sandstone  is not appropriate for limestone. Other arenites include  sandstones ,  arkoses ,  greensands , and  greywackes . Arenites mainly form by  erosion  of other rocks or  turbiditic  re-deposition of sands. Some arenites contain a varying amount of  carbonatic  components a...
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Argillite

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  Argillite   (   / ˈ ɑːr dʒ ɪ l aɪ t / ) is a fine-grained   sedimentary rock   composed predominantly of   indurated   clay   particles. Argillaceous rocks are basically   lithified   muds and   oozes . They contain variable amounts of   silt -sized particles. The argillites grade into   shale   when the   fissile   layering typical of shale is developed. Another name for poorly lithified argillites is   mudstone . [ citation needed ]   These rocks, although variable in composition, are typically high in   aluminium   and   silica   with variable   alkali   and   alkaline earth   cations . The term   pelitic  or  pelite   is often applied to these   sediments   and rocks.   Metamorphism   of argillites produces   slate ,   phyllite , and pelitic   schist . Argillite Sedimentary rock A piece of black arg...
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