Arkose

Classification：Sedimentary Rock

The content of feldspar crumbs is more than 25%, which is generally coarse sand structure with poor sorting and grinding. Its source is usually the decomposed product of granite nearby.

Arkose is a sandstone with more than 25% feldspar crumbs, which includes Arkose and Arkose. It is generally coarse sand structure, flesh red to gray, sorting and grinding degree change a lot. Arkose is mainly composed of felsic parent rocks, such as granite and gneiss, which are mechanically weathered, transported in short distance, and accumulated in Piedmont or mountain basins.

Brief introduction:
Arkose is a sandstone with a feldspar content greater than 25% (in which the quartz content is <75%, which contains more mica and heavy minerals), which includes Arkose and lithic Arkose, and the species of feldspar are mostly acid plagioclase and potassium feldspar. Generally, they are coarse sand texture, flesh red to gray, and the sorting and grinding degree vary greatly, from good to bad. They often contain more hetero groups, and the cements are mostly carbonates, siliceous and iron. When a large amount of quartz debris is contained in the sand (quartz is greater than 75%), it is transition to feldspar quartz sandstone (feldspathic quartz sandstone), or secondary Arkose (subarkose). When the rock contains a lot of hetero group, it belongs to feldspar feldspathic graywacke. Arkose is mainly composed of felsic parent rocks, such as granite and gneiss, which are mechanically weathered, transported in short distance, and accumulated in Piedmont or mountain basins.

Formation:
Although the content of quartz in green ArkoseArkose is more, the content of feldspar can be >25%, even the main component, the content of rock debris is high, the content of heavy minerals can be >10%, and there are many unstable heavy minerals, so Arkose is the sandstone with low mineral maturity. It forms the following conditions:
The condition of the parent rock:
Arkose is mainly composed of feldspar parent rocks, such as granite and granitic gneiss. These rocks can provide large amounts of feldspar after weathering.
Structural conditions:
Arkose requires a large tectonic environment in the earth's crust, which can cause large terrain, which is not only conducive to the exposure of granite, granite gneiss, but also for rapid erosion, rapid transport and rapid deposition of these rocks, so that the unstable feldspar can be preserved.
Climate conditions:
The formation of Arkose requires cold and dry climatic conditions. In this climate, the main physical weathering is physical weathering, and the chemical weathering is very weak. So the weathering of the parent rock mainly provides the broken raw mineral, and the mineral composition is not greatly modified. Therefore, the unstable minerals can be preserved in a large amount, which is beneficial to the formation of Arkose.

Features：
The characteristics of Arkose, such as its name, contain much feldspar, feldspar content is more than 50%, quartz + rock cuttings is less than 50%.
On the one hand, the parent rock contains feldspar, such as feldspar pegmatite.
On the other hand, because the feldspar is easy to hydrolyze, so if Arkose is found, it can indicate that the sandstone has a short moving distance before the diagenesis, and it is easy to form alluvial fan, alluvial fan and so on in the area where the earth's crustal activity is violent, and the internal composition of the inner component is short, so the Arkose is formed.