Negatively Skewed Distributions of Silica and Potassium in Igneous Rocks

Abstract

THE distributions of several elements, including some which are abundant, have been found to be positively skewed in specific igneous rocks^1–6. Many such distributions are either lognormal or approximate lognormality; some may be described as double or multiple lognormal distributions⁷. The most notable exceptions to positive skewness are silica, the most abundant of all constituents, and potassium, each of which has been found to exhibit decided negative skewness⁶. No specific statistical type has yet been assigned to these negatively skewed distributions, a problem which we now consider. We will use the example of silica only, as the distribution of potassium may show closely similar characteristics and can be handled in the same way.