184 Mr. L, Fletcher's Crystallographic Notes, 



(5 1 1) lying in any octant are always striated perpendicularly, 

 or approximately so, to the edges they form with the octahe- 

 dron-face in the same octant: — 



Observed. Calculated. 



111.210 . . 39 53!^ 



4\ 



■3/ 



201.210 . . H Jjj 36 52 



111.511 .. 38 35 38 56 



111.115 . . 55 about 56 15 



The fourth and fifth specimens present crystals very similar 

 to the last, having the habit shown in fig. 5. The observed 

 angles, however, accord better with those of the combinations 

 (111) (5 2 0) (511):— 



Observed. Calculated. 



-, ., . fill. 151 



fourth specimen-j -.,.. - - 1 



Fifth specimen {520' 111 



38 50 38 56 



57 28 56 15 



29 30 30 27 



41 30 41 22 



whilst on the latter specimen four different angles from an 

 octahedron-face to a face of the form (511) in the same 

 octant gave measurements 37° 0', 38° 40', 39° 10', 39° 15' 

 respectively, the calculated angle being 38° 56'. 



II. Silver. 



The following forms have already been described as occur- 

 ring on native silver: — 



(100) (110) (111) (210) (520) (410) (211) (311). 



The form (7 51) has been observed by Dauber* on an arti- 

 ficial crystal. The forms (2 1 0), (5 2 0), (4 1 0), (2 1 1) have 

 not been observed on any of the crystals in this collection. 

 The form (211) is given by Groth in his Catalogue of the 

 Strassburg collection, but is possibly a misprint for (311): 

 (5 2 0) was observed by Sadebeck f; the forms (2 1 0) (4 1 0) 

 have been confirmed by the same crystallographer. To the 

 list of observed forms must now be added (3 1 0) and (7 4 0). 



A specimen, originally labelled "Arquerile, Chili," but from 

 which analysis proves the entire absence of mercury, consists 

 of a group of beautiful crystals of native silver associated with 

 cerargyrite and crystallized calcite in a limestone cemented 



* Annalen der Chemie und Pharmacie, vol. lvii. 1851. 

 t Tschermak, Mineral. MittJieil 1878, p. 293. 



