(Table 2) Chemical composition of potassium feldspars from DSDP Hole 19-192A

Secondary potassium feldspar (K-feldspar) in oceanic basalts represented by low-temperature sanidine with low content of albite molecule. K-feldspar replaces nucleus of phenocrysts and large microlites of plagioclase. Occurrence of K-feldspar increases with age of rocks; in Pliocene and Pleistocene basalts from zones of mid-ocean ridges K-feldspar is absent. K-feldspar is developed in basalts of various geological, textural and structural types. Correlation of K-feldspar occurrence with primary alkalinity of basalts is absent. High (1-6%) contents of K2O in basalts in almost all cases are associated with development of K-feldspars in them. In basalts containing K-feldspars, a clear correlation between K2O and H2O (R = 0.55) is observed.