Sandstone arkosic arenite

Microlithofacial classification of the sandstones is based on Dott s classification modified by Pettijohn et al. (1972). They are mostly arenites and subarkose and quartz wackes (rare sublithic, sporadically lithic and arkosic). Quartz is the main component of the sandstones (about 60-70 vol. percent). Feldspars (6 vol. percent) are mostly represented by potassium feldspars with plagioclases in lesser amounts. Some micas (muscovite and biotite) and chlorites are observed. Mica content of arenites reaches 3 vol. %, but is higher in the wackes. Heavy minerals present include zircon, sphene, rutile and apatite. Magmatic rocks (volcanic more than Plutonic) are predominant among lithoclasts (about 2 vol. %), but some metamorphic and sedimentary clasts being present too. 

There are a few other terms commonly used to describe sandstones. A wacke is a poorly sorted sandstone containing more than 10% argillaceous material (clay). Arenites are well-sorted sandstones having little or no clay in them. An arkose is a sandstone whose particles are derived from plutonic rocks and so consist largely of quartz and feldspar. 

Fig. 7. QFR triangular diagram of sandstone petrography of Folk (1974). Q, quartz F, feldspar R, rock fragments. 1, quartz arenite 2, subarkose 3, sublitharenite 4,5, arkose 6,7, litharenite.

In other words, those sandstones with more than 15% matrix were termed wackes. The chief type of wacke is greywacke, which can be subdivided into lithic and feldspathic varieties. Those sandstones with less than 15% matrix were divided into three families. The orthoquartzites or quartz arenites contain 95% or more of quartz 25% or more of the detrital material in arkoses consists of feldspar and in lithic sandstones, 25% or more of the detrital material consists of rock fragments (Fig. 1.20). 

Sandstone Grains are mainly mineral fragments Quartz arenite 95% quartz, voids empty or cemented Arkose 75% quartz, up to 25% feldspar voids empty or cemented... 

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