The major elements in common rocks are of low atomic number, butanalyses of high precision are possible by soft X-ray spectrography if several grams of rock sample are available. The electron-probe microanalyzer is shown to complement this established method by permitting analyses of particles as small as 1 p. in diameter. This paper describes applications of these methods to the analysis of the major and minor elements of silicate, carbonate, and phosphate minerals and rocks. Elements of particular interest are as follows: carbon in particles enclosed in carbonate rocks; oxygen, as the major constituent of the specimens; phosphorus in phosphatic nodules and apatites; manganese andiron, as colorations in fossil shells; and the group oxygen, sodium,magnesium, aluminum silicon, potassium, calcium and iron as complex segregations and zonations within single crystals of several mineral phases. If the bulk composition of a rock is known, and also the chemistry of the constituent minerals, it is possible to compute quantitative mineralogic analyses of high precision. Thus, the combined use of soft X-ray spectrography and electronprobe microanalysis can provide quantitative chemical and mineralogical information on the earth's crust on all scales from thousands of square miles (by means of appropriate sampling) down to the scale of 1mu.