A shallow metamorphic rock. It is formed by the slight metamorphism of clayy, silty sedimentary rocks or medium-acidic tuff rocks and sedimentary tuff. Black or grayish black. The lithology is dense and the plaque is developed. There are often a small amount of minerals such as sericite on the surface of the board, which makes the surface of the board slightly lustrous. There is no obvious recrystallization. Under the microscope, some mineral crystals such as quartz, sericite and chlorite are distributed unevenly, but most of them are cryptocrystalline clay minerals and carbonaceous and iron powders. It has a variable structure and a speckled structure. Common types are carbonaceous slate, calcareous slate, black slate, etc.; also according to Other characteristics of rock, such as mineral composition, structural structure, etc., divided into anaconite slate, spotted slate, silty board Rock, silicon slate, etc. The slate is widely distributed in the rock series with low-temperature dynamic metamorphism. For example, the bean slate of the Early Yuan Dynasty ancient shoal group in northern China, and the Banxi group and the Kunyang group in the southern middle and late Proterozoic are also distributed. Can be used as building stone.
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