Till! TKICI.INIC SYS' II M 



I'J'.I 



In thr tri;mgl<' doe, right-iinglrd at o and with theside oe = b = 

 i ;ind the angle ode known : 



1 = = C ot ode = cot 56 37' = .658 * or a = .658 *. 

 oe b 



For the value of c the angle (001 ,101) = 50 16'. 

 In the triangle coa, p = 63 37' and oca = 180 - (50 16') - 

 (63 37') = 65 47'. 



In the triangle aoc, in which the angles and one side oa = a = 

 .658 + are known, oc = c may be calculated, 

 oc : oa : sin oac : sin oca, or c : a : : sin 59 16' : sin 65 45'. 



c = 



a X (sin 59 16') 



sin (65 45') 

 Log a =1.818226 

 Log sin 50 16' = 9.885942 

 9.704168 



Log sin 65 45' = 9.959852 

 Log c = 1.7443 16 

 c= .555 + . 



The crystalline constants of orthoclase would be expressed as 

 calculated, * : b: c = ,658+ : 1 : .555+ : p =- 63 57'. 



THE TRICLINIC SYSTEM 



In the triclinic system all axes are inclined, and none of the five 

 crystalline elements are fixed ; the axes are unequal and designated, 

 ft: b: c, as in the orthorhombic system. Generally the unit plane 

 has been chosen so that the unit on c is smaller than that on b, 

 but this may not be so in all species. Here the diametral planes 

 divide space into octants of four different sizes ; of which opposite 

 octants through the center are similar; thus the pyramids of the 

 triclinic system will consist, at the most, of a single pair of parallel 

 faces each subtending octants of the same size. The four possible 

 pyramids are equivalent to the orthorhombic pyramid and in 

 combination inclose space. The axial angles are either greater 

 or less than 90 and are measured in the plus octant, the upper right- 

 hand octant. The angle between b and <i is designated a, that 

 between & and b, "y, and that between & and c, P, Fig. 265. 



