The color ratio of andesite is generally 20 to 35. The hand specimens are gray, black, red, purple, brown, etc., and are green and plaque-like after alteration. The phenocrysts are mainly plagioclase and dark minerals. Among them, plagioclase is mainly composed of medium feldspar and labrador, and often has an annulus and an ablated structure. Common dark minerals are pyroxene (common pyroxene, perilla pyroxene), hornblende and biotite. The matrix is ​​mainly composed of interwoven structure and Anshan structure (glass-based interwoven structure), which consists of plagioclase (longer and medium feldspar) microcrystals, pyroxene, chlorite, and Anshan glass. Feldspar and quartz are rare and are only filled in the microcrystalline gap. The secondary minerals are mainly apatite and iron oxides. Stomatal, massive structure, some pores are filled with calcite, quartz, chlorite, etc., forming an almond structure.
The SiO2 content in the porphyrin andesite in Andesite and Anshan rocks varies greatly (52~63%), and the average content is 58.17%. 98.5% of Andesite's SiO2 is supersaturated with standard mineral quartz (less than 15%). Andesite can be divided into two types according to SiO2 content: 52~57% of Xuanwu Andesan; 57~63% of Andesite, Andesite's Litman index, ie (K2O+Na2O)2/(SiO2-43) ratio Generally less than 3.3, it is calc-alkaline. The average chemical composition of andesite is SiO2=52.4%, Al2O3=17.17%, CaO=7.92%, Na2O=3.67%, K2O=1.11%, lower SiO2, higher CaO, all The base is less than 5.5%, and Na2O>K2O is characteristic. Andesite and basalt are often difficult to distinguish. It is generally believed that SiO2 is >52%, and the color ratio is <40% for andesite; the other is basalt.
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