2-D and 3-D Trend Analysis - Geomathematics: Theoretical Foundations, Applications and Future Developments - page 239

Fig. 7.3 Quadratic (subscript 1) and cubic (subscript 2) trend surfaces for (a) percent forsterite in olivine, (b) percent enstatite in orthopyroxene, and (c) cell
edge, chrome spinel. Patterns for Mg content in olivine and orthopyroxene are similar in shape but variation is more pronounced in orthopyroxene (steeper
gradients). Area measures 10.6 km in east-west direction (for scale see Fig. 7.5 ) (Source: Agterberg 1974 , Fig. 42)