sodic series

The term "sodic series" refers to a subdivision within the calc-alkalic series of igneous rocks. This classification is based on the relative proportions of soda (sodium) and potash (potassium).1

Igneous rocks are categorized by their mineral content, chemistry, and texture. Volcanic and hypabyssal rocks, which cool quickly, are often classified by their chemical composition because their fine-grained texture makes mineral identification difficult. The sodic series is part of the subalkaline group, which is characterized by rocks that are saturated with silica. These rocks typically contain normative minerals like orthopyroxene and quartz, and lack nepheline and olivine when quartz is present.1

Sodalite, a feldspathoid mineral, is found in igneous rocks like nepheline syenite, trachyte, and phonolite, which are types of alkaline rocks. Alkaline rocks are distinguished by a high content of alkalies (potassium and sodium oxides) relative to silica.23