28 EII0MB0IIEDKAL SYSTEM. 105. In the form Xhkl (fig. 40), sinJ-n = cos-’l cos<p, cosiy = cos sin (45°+ <j>). ., 10 , Q ' In combinations of the form XhM with the form 110, the laces of 110 truncate the edges v. 107. In the form nkkl (fig. 4i)-, cosm = (singi)’. 108. In the form alkl (fig. 42), cosm = (sin *l)% cos|t = COS-gLCOS^, , . cos|y = cos|l sin (45°+ <f). combinations of the form ahkl with the forms 100, HO, the faces of 100 truncate the edges t ; and the faces of 110 truncate the edges v. ftg. 40. FIG. 41. FIO. 42. 110. The cleavages, in crystals belonging to the pyramidal sys em, are parallel to the faces of one or more of the forms 001, ioo, hoi, Mil. IUIOMBOHEDEAE SYSTEM. with on*u. e r k om b°hedral system the axes make equal angk with each ether, and the parameters arc equal. 1 b their~svmt\m °ei l vl* bounded by all the faces which have fc In this case n e W when the indices are 0, - 1, j n also when two of tho indices are equal, tl:
