﻿E. S. Dana — Crystallization of Gold. 



137 



It was suggested by Naumann,* that 15-f (15*9 1) was a more 

 probable symbol, since it satisfied the measured angles about 

 as well as the other, and at the same time was a form whose 

 edges (A) were truncated by the common trisoctahedron 3-3 

 (311). This suggestion Rose was inclined to accept, and later 

 writers have followed him (e. g. Klein).f A comparison 

 between Rose's angles and those required by the form 18-f 

 (18 # 10*1), positively determined on the California crystals, leaves 

 no doubt that the latter symbol should also be given to Rose's 

 plane since it satisfies the measured angles as well or better 

 than either of the others suggested. 



Calculated. 

 Edge B. 





Measured. 

 Rose. 



15-$ 



6° 33' 



18-| 

 5° 34' 



5° 10 to 5° 41' 



For 19-ff- 

 5° 13' 



Inclination on o (111) 

 35° 28' 34° 32' 35° 41 -J- 36° 50' to 37° 10' 



On d(110) 

 15° 9' 14° 24' 16° 11' 15° 30' to 15° 50' 



This is an interesting example of a case in which the so- 

 called zonal law, so often employed to decide a doubtful symbol 



does not hold good. Figure 6 shows one form of the crystals 

 now being described ; another is given in figure 7 which also 

 exhibits an additional point of interest. The octahedral edge 

 is here, in some cases, apparently truncated by the dodeca- 

 hedral plane, in others beveled by a pair of planes ; closer 

 inspection, however, shows that this edge is formed simply by 

 an oscillatory combination of the adjacent planes of the hex- 

 octahedron. In other crystals of more octahedral habit the 

 edges are all thus finely striated. The faces of the trisocta- 

 hedron m are also, though not always, striated in a similar 

 manner, and sometimes the place of the plane seems to be taken 

 by this oscillatory combination of the hexoctahedral planes. 

 This hexoctahedron x, 18-}, appears to be a common form 



* Pogg. Ann., xxiv, 385. 



f Jahrb. Min., 1872, 129. 



