31. Huntite crystallizes in the trigonal system and typically occurs as platy crystals and powdery masses. 32. In this structure, nickel is octahedral and the selenides are in trigonal prismatic sites. 33. There are three special case geometries of the " diminished trigonal trapezohedron ". 34. Two are in approximate tetragonal pyramids and the third is essentially a trigonal bipyramidal coordination. 35. Magnesite consists of white trigonal crystals. 36. If the crystal system is not trigonal then the lattice system is of the same type. 37. Smithsonite is a variably colored trigonal mineral which only rarely is found in well formed crystals. 38. It has a trigonal pyramidal shape. 39. The crystal system is a trigonal -rhombohedral class 3 and has space group of R. 40. Why can't trigonal bipyramids?
