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The planes of this form are similar to trapeziums. Because it has twenty-four sides, it is usually called the Icositetrahedron. Its solid angles are of three kinds: six tetrahedral at the ends of the principal axes; twelve tetrahedral at the ends of the digonal axes; ans eight trihedral at the ends of the trigonal axes. There are twenty-four octahedral and twenty-four cubic edges. Naumann's symbol for this form is m0m; Dana's is m-m.

Icositetrahedron

The planes of this form are similar to trapeziums. Because it has twenty-four sides, it is usually called…