Measure the intercepts of each mineral along a series of lines. The number of grains counted, the spacing between points and successive traverse lines is dependant on the mean grain size of the sample. Advantages One can compare rocks from different areas if you only have a thin section, no chemical analysis is required, using a petrographic microscope. Gives the maximum and minimum grain sizes. Disadvantages Meaningless if the sample has a preferred orientation of one or more minerals.
Porphyritic rocks are difficult to count.
Total area of sample must be sufficiently larger than the max.