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Soil Survey Manual - Table 3-13

Size classes of soil structure

Shape of structure
Size Classes Platy1
mm		 Prismatic and Columnar
mm		 Blocky
mm		 Granular
mm
1 < 1 < 10 < 5 < 1
2 1 - 2 10 - 20 5 - 10 1 - 2
3 2 - 5 20 - 50 10 - 20 2 - 5
4 5 - 10 50 - 100 20 - 50 5 - 10
5 > 10 > 100 > 50 > 10

1. In describing plates, "thin" is used instead of "fine" and "thick" instead of "coarse."