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Definition of argillaceous rock

Definition of argillaceous rock

Definition of argillaceous rock


Would anybody know if there is any documentation or report that lists a content of argillaceous material in a rock that deems it a argillaceous rock

It seems that the statement argillaceous rock is very commenplace but their is very little documentation in the specifications

RE: Definition of argillaceous rock

Encyclopedia Brittanica contains the following article (citation at the end of the article):

In terms of volume, mudrocks are by far the most important variety of sedimentary rock, probably constituting nearly 80 percent of the Earth's sedimentary rock column. Despite this abundance, the literature on mudrocks does not match in extent or detail that dealing with sandstones, carbonate rocks, and the various rarer sedimentary rock varieties like evaporite and phosphorite. This paradox reflects the difficulties inherent both in analyzing such rocks, owing to their poor exposure and fine grain size, and in interpreting any data obtained from their analysis because of the effects of diagenesis. Mudrocks include all siliciclastic sedimentary rocks composed of silt- and clay-size particles: siltstone (1/16 millimetre to 1/256 millimetre diameters), claystone (less than 1/256 millimetre), and mudstone (a mix of silt and clay). Shale refers specifically to mudrocks that regularly exhibit lamination or fissility or both. Mudrocks are also loosely referred to as both lutites and pelites and as argillaceous sedimentary rocks.

Though mudrocks are composed mainly of detritus weathered from preexisting rocks, many contain large amounts of chemically precipitated cement (either calcium carbonate or silica), as well as abundant organic material. Mudrocks produced from the alteration of volcanic lava flows and ash beds to clay and zeolite minerals are called bentonites .

General properties of shales
The properties of shales are largely determined by the fine grain size of the constituent minerals. The accumulation of fine clastic detritus generally requires a sedimentary environment of low mechanical energy (one in which wave and current actions are minimal), although some fine material may be trapped by plants or deposited as weakly coherent pellets in more agitated environments. The properties of the clay mineral constituents of lutites are particularly important, even when they do not make up the bulk of a rock.

The mineralogy of shales is highly variable. In addition to clay minerals (60 percent), the average shale contains quartz and other forms of silica, notably amorphous silica and cristobalite (30 percent), feldspars (5 percent), and the carbonate minerals calcite and dolomite (5 percent). Iron oxides and organic matter (about 0.5 and 1 percent, respectively) are also important. Older estimates greatly underestimated clay minerals because of incorrect assignment of potassium to feldspar minerals. The most abundant clay mineral is illite; montmorillonite and mixed-layer illite-montmorillonite are next in abundance, followed by kaolinite, chlorite, chlorite-montmorillonite, and vermiculite. The quartz-to-feldspar ratio generally mirrors that of associated sands. In pelagic (deep-sea) sediments, however, feldspar may be derived from local volcanic sources, whereas quartz may be introduced from the continents by wind, upsetting simple patterns. A large number of accessory minerals occur in shales . Some of these are detrital, but diagenetic or in situ varieties (e.g., pyrite, siderite, and various phosphates) and volcanically derived varieties (e.g., zeolites, zircon, and biotite) have been noted.

"Sedimentary Rock." Encyclopædia Britannica. 2003.  Encyclopædia Britannica Premium Service.
25 Jun, 2003  <http://www.britannica.com/eb/article?eu=117862>;.

I hope this helps -

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