31. It crystallizes in the tetragonal crystal system and forms as rounded dissemations within tetrahedrite in quartz veins. 32. "' Eskebornite "'is a tetragonal system and it has a brassy colour. 33. Those minerals have same chemical composition but different crystal symmetry : orthorhombic for columbite and tetragonal for tapiolite. 34. This transition results in a change in the fourfould axis of the tetragonal cell, causing Crystal twinning. 35. It crystallizes in the tetragonal trapezohedral class and is one of only a few minerals in that class. 36. Those minerals have same chemical composition, but different crystal symmetry orthorhombic for tantalite and tetragonal for tapiolite. 37. Crookesite is an opaque, bluish grey to pink toned brown metallic mineral crystallizing in the tetragonal system. 38. Trigonal, tetragonal and hexagonal crystals have a single optic axis, parallel to the c crystal axis. 39. This polyhedron can be constructed by taking a tetragonal trapezohedron and kite faces of the trapezohedron become pentagons. 40. It is a brightly light, tetragonal pyramid and seemly serves no purpose other than an artistic one.
