Calcium Phosphate, Apatite
This crystal of Calcium Phosphate, Apatite, represents a complex combination of hexagonal hemihedral forms produced by the pyramidal selection. The nine forms comprise the basal pinacoid ,(P); the prism of the first order, (M); second order, (u); and third order, (h); three pyramids of the first order, (r), (x), and (y); one pyramid of the second order, (s); and one of the third order, (m).
George Huntington Williams, Ph.D. Elements of Crystallography for Students of Chemistry, Physics, and Mineralogy (New York, NY: Henry Holt and Company, 1892)