Phyllite

Classification：Metamorphic Rock

The metamorphic degree is between the slate and the schist. The typical mineral assemblage is sericite, chlorite and graphite, which makes the cleavage masks lustrous and the part of the schist coarser.

Phyllite is a low-grade metamorphic rock with dry texture. The protolith is usually composed of argillaceous rock, siltstone and intermediate acid tuff. It is formed by regional low-temperature dynamic metamorphism or regional dynamic heat flow metamorphism. The micro wafer surface is variable with hair silk. The degree of metamorphism is between the slate and the schist. Often changing crystal structure for fine scales, particle size less than 0.1 mm in the schistosity surface often small wrinkle structure.

Features：
Phyllite is a low-grade metamorphic rock with thousand grain structure. The original rocks are usually muddy rocks (or siliceous, calcareous, carbonaceous argillaceous rocks), siltstone and intermediate and acidic tuff, which are formed in the phase of the bottom greenschist facies by regional low-temperature dynamic metamorphism or regional dynamic heat flow metamorphism. The micro wafer surface is variable with hair silk. The degree of metamorphism is between the slate and the schist.
Phyllite lithology is soft and water is easy to slime and soften (also known as soft rock). It has shrinkage property and poor engineering geological properties, which will lead to large deformation. Weathering resistance is poor, weathering is easy to form cuttings, resulting in fragmentation.

The main rock types of Phyllite:
Sericite Phyllite, green mud Phyllite, quartz Phyllite, calcareous Phyllite, carbonaceous Phyllite and so on.

Mineral composition:
The typical mineral assemblages are sericite, chlorite and quartz, which contain a small amount of feldspar, carbon and iron. Sometimes there are small amounts of calcite, biotite, black chlorite or manganese garnet. Often changing crystal structure for fine scales, the particle size is less than 0.1 mm, the schistosity surface often small wrinkle structure. The protolith is clay, siltstone or intermediate acid tuff. It is a product of low-level regional metamorphism. Because of different original rock types, mineral assemblages are also different, resulting in the formation of different types of Phyllite. For example, the clay rock can form the Phyllite of the hard chlorite, the siltstone can form the quartz Phyllite, the acid tuff can form the sericite Phyllite, and the middle base tuff can form the chlorite Phyllite and so on. Phyllite can be further divided into silver gray sericite Phyllite, gray black carbonaceous Phyllite and gray green hard chlorite Phyllite according to color, characteristic minerals, impurity components and major scale minerals. Phyllite is widely distributed and can be formed in different geological ages.