Figure 2.
(A–C): Modeled basaltic “rocks” of varying grain size: red—glass, blue—olivine, purple—plagioclase, and pink—augite. Black squares are the sampling areas (50). Grain size relative to beam size increases to the right; beam size remains constant at 40 pixels. (A) Grain size = 10 pixels. (B) Grain size = 50 pixels. (C) Grain size = 150 pixels. (D–F): Comparison of true versus calculated bulk composition as grain size increases relative to beam size, with grain size < beam size (0.25), grain size ≈ beam size (1.25), and grain size > beam size (2.5). The solid line denotes where grain size and beam size are of equal size. Dashed lines represent the true electron probe microanalysis–determined bulk composition. Circles are the calculated values. (D) MgO. (E) Al2O3. (F) CaO.