Graywacke

Classification：Sedimentary Rock

Sandstone with a clay content greater than 15%, poor sorting, low structural maturity and mixed sediment is a density flow deposit.

Graywacke is defined as a sandstone with a clay content of more than 15%, with poor sorting, low structural maturity and mixed sediment. It belongs to density flow deposition. Graywacke is usually rich in quartz with a content of up to 50%. Quartz generally has edges and corners, and often has obvious wave extinction. Classification is the same as pure sandstone. The principle of further classification and naming is the same as that of pure sandstone.

Brief introduction:
Graywacke is also called greywacke. Stone refers to sandstone with a content of more than 15% of clay matrix. The main components are quartz, feldspar and cuttings, and they can also contain muscovite, biotite and chlorite and other carbonate minerals such as calcite and dolomite, and the composition of heavy minerals is complex. Graywacke is usually dark brown, gray green or black, and is generally a well consolidated hard sandstone. It often forms a rhythmic layer with siltstone and argillaceous rock in strata. According to the relative content of quartz, feldspar and cuttings, three kinds of quartz can be divided into three types: quartz Graywacke, feldspar Graywacke and debris Graywacke. Graywacke is formed in the strong belt of tectonic movement, and it is fast after mechanical erosion. [1]

Main features:
The main features of Graywacke are dark, tough, and well consolidated and contain a variety of debris, mainly silty and low metamorphic cuttings. Acid volcanic debris is common, quartz content is up to 1/3 to 1/4, feldspar is mainly sodium feldspar, containing sericite, chlorite, epidote and other inclusions. The debris particles are angular and the separation is very poor. It indicates that the English graywacke of Graywacke is originally a shallow metamorphic and poorly sorted lithic sandstone. This rock is mostly produced in the flysch formation of sedimentary basin with active tectonic activity.

Mineral composition:
Graywacke often contains different ratios of feldspar and debris, and there are very few mica crumbs.
The feldspar is mainly plagioclase and rare potash feldspar. In the younger sandstone of geological age, the mixed acid plagioclase and basic plagioclase are seen, but in the old rocks, the common albite, orclite and acid feldspar are common, and the partial plagioclase is unstable and very rare. Some sandstones contain zeolite, zeolite calcium may be speculated that this altered the formation of calcium feldspar. Feldspars are usually fresh, but some feldspar grains are usually cloudy and form some alteration products.
The cuttings are mainly shale, siltstone, slate, phyllite and mica schist, and flint and fine-grained quartzite and polycrystalline quartz are also abundant. Some sandstone contains fine-grained volcanic debris with feldspar microcrystals, of which relatively common bolt volcanic debris and rare Anshan debris.
Mica detritus is commonly found in Muscovite and biotite, and chlorite in biotite.

Distribution and formation:
Graywacke sandstone with poor sorting and sand mixing is usually more quartz and more angular. Feldspar and cuttings with different ratios often contain a small amount of mica. The feldspar is mainly plagioclase, with a variety of cuttings. Hetero group is the basic feature of Graywacke. The smaller the particle is, the higher the content of hetero group is. Matrix components in chlorite, mica common. The formation conditions of Graywacke are similar to that of feldspar sandstone or lithic sandstone, that is, rapid erosion, transport and deposition, but Graywacke can be formed under different climatic conditions. Typical Graywacke often accumulate in rapidly settling turbidite or flyback formation.