Chemical classification of common volcanic rocks based on degree of silica saturation and CaO/K2O ratio

Modal classifications of common volcanic rocks are expensive, difficult, or impossible to attain. As a consequence, these classified using the chemical composition. However, existing classificatory diagrams unable identify all 16 families rocks; most used is total alkali-silica (TAS) diagram that identifies six families. Rocks not in TAS misclassified with other rock names; their names evolving extinction, e.g. latite and rhyodacite. Some use Na2O, which complicating element rather than discriminant. Na2O present both alkali feldspar plagioclase making difficult separation amount associated either feldspar. Silicon, potassium, calcium three major elements highest variations among rocks. They selected for two new confronting CaO/K2O ratio K2O content (KCK diagrams). One designed saturated (intermediate) (quartz <5 vol.%) oversaturated (acid) >5%). These tested compositions from Uatumã magmatism Amazon Craton also by plotting type-localities world averages. The proposed limits between agree plotted compositions. KCK an alternative classify