Lutite

Lutite is any sedimentary clastic rock with clay or silt grain size less than 1/16 mm (0.06 mm or 0.00256 in). [ [http://concise.britannica.com/ebc/article-9370752/lutite Britannica definition of "lutite"] . Accessed on December 31, 2007]

The term is used in the classification of clastic carbonatic limestones, as the granulometrically equivalent term siltstone or claystone is not appropriate for limestone.

Lutites mainly form by erosion of other rocks or turbiditic re-deposition of clays or muds. Some lutites contain a varying amount of carbonatic components and thus belong to the rock-category marl. Lutites often appear as massive or layered (laminated) fine-grained rocks without preferred fissility. Depending on grain size composition lutites are called claystones, siltstones or mudstones. Lutites subjected to compaction by load or tectonic stress develop a preferred fissility and are called shales. [ [http://concise.britannica.com/ebc/article-9378384/shale Britannica definition of "shale"] . Accessed on January 1, 2008]

Pettijohn [Pettijohn F.J. (1975), "Sedimentary Rocks", Harper & Row, ISBN 0-96-045191-2] gives the following descriptive terms based on grain size, avoiding the use of terms such as "clay" or "argillaceous" which carry an implication of chemical composition:

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