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E. S. Dana — Crystallization of Gold. 



The planes 113, 311, 131, with the three opposite, form an 

 obtuse rhombohedron with the symbol \-R (2025) and having a 

 terminal angle (supplement) of 50° 29'. The six adjoining 

 planes, 1I3, 311, 311, 131, 131, 113, with their opposites, form a hex- 

 agonal pyramid of the second series, with the symbol f-2 (2243) ; 

 the terminal angle is here 50° 29' and the basal angle 62° 58'. 

 The six remaining planes of the twenty-four, namely 113, 311, 131, 

 and those opposite, form an acute rhombohedron with a symbol 

 4:R (4041), and a terminal angle of 117° 2'. 



The predominating form is uniformly this last mentioned 

 acute rhombohedron ; though traces of the pyramid can usu- 

 ally be seen. The simple crystalline threads are built up of 

 a series of these rhombohedrons in parallel position and 

 crowded closely together. This is shown in fig 4. The ter- 

 minal crystal is often larger than the 

 others, and frequently of the skeleton 

 type with prominent salient edges and 

 the larger part of the face depressed, 

 and perhaps made up of a series of 

 fine parallel wires of frosted gold, 

 suggesting some of the most delicate 

 ornaments made by a skillful worker 

 in gold. 



The threads, however, are not lim- 

 ited to a single line of parallel crys- 

 tals ; generally there are two lines 

 close together with a depressed furrow 

 between them, and a third in which 

 the crystals are also in parallel po- 

 sition with each other, but elon- 

 gated according to another octahedral axis. In these last 

 cases each plane of a crystal in one line is parallel to one in the 

 other, but these planes have a different value in the rhombo- 

 hedral development. Figure 5 shows a string of these crystals 



