21. It crystallizes in the tetragonal crystal system. 22. Each vertex is surrounded by 4 truncated tetrahedral cells in a tetragonal disphenoid vertex figure. 23. If between . 71 and . 9, the crystal will be orthorhombic or tetragonal . 24. Two are in approximate tetragonal pyramids and the third is essentially a trigonal bipyramidal coordination. 25. Between 0.7 and 1.1 GPa the clathrate has a tetragonal structure. 26. It crystallizes in the tetragonal system and occurs both in good crystals and as formless masses. 27. The tetragonal form is called litharge. 28. More complicated aggregations have also been observed, such as rhombohedral, tetragonal and orthorhombic phases. 29. The mineral is classified under the space group P4 1 2 1 2 and is tetragonal . 30. Well known crystalline forms are ?-rhombohedral, ?-rhombohedral, and ?-tetragonal .
