Quantitative mineralogical analysis of grain mounts results in either a number percentage or a number frequency. The number percentage is obtained when all the grains on the slide or all the grains in representative portions of the slide are counted. The number percentage is solely a function of the numerical abundance of the mineral grains on the slide. The number frequency is obtained when the grains on the slide which intersect the cross hairs along linear traverses are counted. The number frequency is a function of both the numerical abundance of the mineral grains and the grain size but is distinctly different from either number percentage or area percentage.