Mr. L. Fletcher's Crystallographic Notes. 181 



were always twinned, and their faces dull and not very plane. 

 Schrauf * has observed the same form on some artificial crys- 

 tals of this metal. The same mineralogistf describes crystals 

 from Wallaroo in South Australia which exhibit the hemihedral 

 form 7r(2 1 0). ZerrennerJ has observed an imperfect deve- 

 lopment of this hemihedral form on a crystal from Bolivia, 

 whilst a second crystal on the same specimen presented the 

 combination of (2 1 0) with slight (4 1 2) and (1 1 0). The 

 form (18 10 5) was observed by Vom Rath § on crystals of 

 a specimen from Lake Superior. The form (3 1 0) was ob- 

 served (1877) by Jeremejew|| on some crystals from Syryanow 

 in the Altai district; and he incidentally remarks that, of all 

 the native metals or alloys, it has only been met with on amal- 

 gam. We shall see later that it also occurs on both native 

 silver and native gold. 



To the list of observed forms must now be added 



(410) (530) (730) (740) (411) (511) (531). 



The form (3 1 0) has also been observed on crystals from 

 other localities than the above. 



Where not stated to the contrary, the instrument employed 

 for the determination of the angles was a reflecting gonio- 

 meter. As images often could not be obtained, the position of 

 a face was in general determined by its maximum illumina- 

 tion. For more accurate determination of the angles, in some 

 cases the faces were slightly oiled, while in others thin reflect- 

 ing plates were fixed upon them. A few of the observed and 

 calculated angles are given in each instance. 



In the case of some of the above new forms the indices have 

 been marked on the crystals for some years : they are con- 

 firmed by the measurements given below. 



A crystal removed from a specimen from Lake Superior 

 presented a symmetrical development of the combination 

 (100) (110) (310):— 



Observed. Calculated. 



310.310 . . 36° 30 / -37° 20' 36° 52' 

 310.110 . . 25° 15' 26° 34' 



A specimen, from the Bank Mines near Ekaterinburg is a 

 fine ramose mass of crystals, in a matrix of grey crystalline 

 limestone. Some of the crystals present the combination 

 (111) (100) (110) (310), much shortened along a tri- 

 gonal axis: — 



* Tschermak, Mineral MUtheil. 1873, p. 290. 

 t Ibid. 1872, p. 53. % Mid. 1874, p. 94. 



§ Groth's Zeitschrift fur Krystallographie, 1878, p. 169. 

 II Ibid. 1877, p. 398. 



