Elements of mineralogy, crystallography and blowpipe analysis from a practical standpoint .. . The values of nS. and mc may be determined from any two ofthe angles X, Y, Z, Fig. 184,by equations like the following : cos « = cos \Xsin^|z cos \Zcos /9 = 2— sin J A na = cot a. mc = tan /9 x nd. Evidently a rhombic pyramid may be composed either of faceswith the unit intercepts, or the faces may be at other angles. 50 CRYSTALLOGRAPHY. with any one or two of the intercepts simple multiples of the unitintercepts. Three types are distinguished, the symbols being :* series Pyramids, a:h:mcM
Elements of mineralogy, crystallography and blowpipe analysis from a practical standpoint .. . The values of nS. and mc may be determined from any two ofthe angles X, Y, Z, Fig. 184,by equations like the following : cos « = cos \Xsin^|z cos \Zcos /9 = 2— sin J A na = cot a. mc = tan /9 x nd. Evidently a rhombic pyramid may be composed either of faceswith the unit intercepts, or the faces may be at other angles. 50 CRYSTALLOGRAPHY. with any one or two of the intercepts simple multiples of the unitintercepts. Three types are distinguished, the symbols being :* series Pyramids, a:h:mcMacro Pyramids, d : nb\ mc Brachy Pyramids, iia? mc Dana. mm — nin — « { hhl\\ hkl \\ khl \ Limit Forms. The general form for special positions of the faces may be-come one of six limit forms, as follows : Each face parallel to two axes. Weiss. d : (xib : c oa : (X b : oii c i — i 1. Basal Pinacoid. 2. Macro Pinacoid. 3. Brachy Pinacoid. 00 Each face parallel to one axis. 4. Brachy Dome. 00 a : 5. Macro Dome. a: oob\mc d : nb : ca cn d:b : ca c 6. Prism. d
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