348 Palache and Wood — Crystallographio Study of Millerite. 



dron, e, (0112), the latter identical with the gliding plane. 

 !N"o difference in the quality of the two cleavages can be 

 detected, and planes of both are generally produced when a 

 crystal is broken. No indication of a cleavage parallel to a 

 prism, such as Laspeyres found in millerite derived from 

 beyrichite, was observed. 



The Orford millerite is characterized by brilliant metallic 

 luster, and a pale brass-yellow color which is quite constant on 

 all planes and surfaces of the mineral. Laspeyres' conclusion 

 mentioned above, that all millerite is derived from beyrichite, 

 a conclusion based largely on an observed color change, finds 

 absolutely no support in this occurrence. 



No analysis of the millerite was made. Careful qualitative 

 tests for copper and cobalt gave only negative results, and it 

 is probably very nearly pure nickel sulphide. 



Cry st a llography. 



A number of crystals showing natural terminal planes were 

 obtained from several of the specimens by removal of calcite 

 with hydrochloric acid. In the majority of cases, the crystals 

 were attached to the matrix by an end and thus showed but a 

 single termination ; two or three crystals of poor quality 

 were found which were attached by prism faces and thus 

 showed both terminations. These crystals were in all cases 

 small, from 2 to 5 mm in length, and from 0'l mm to l mm in dia- 

 meter. In habit they vary from slender prisms to short stubby 

 crystals of diameter equal to or greater than their length. 



In all thirty-two crystals were measured. Of these twenty- 

 eight were measured completely in the two-circle goniometer. 

 Four were measured for special angles. 



From the data obtained in measurement, the following forms 

 were established, those marked with a_star being_new : 5, (10l0), 

 a, (1120), k, (2130), d, (7290*), r, (1011), v n (5052), p, (0221*), 

 s, (2131*) and u, ($153*). Doubtful values for the following 

 forms were found. These need confirmation_for their estab- 

 lishment, i, (4150),/, (94-13-0*), g, (3L13-44-0*), t, (_0_33l), 

 A, (3031*), x, (4011*), j, (5051*), I, (0991*), m, (0-18-18-1*), 

 n, (5276*). o, (T4-11-9*), q, (5174*), and w, (4265*). The 

 only forms satisfactorily established which we did not find on 

 the Orford mineral are the base c, (0001), which was observed 

 by both Miller and Laspeyres, and the rhombohedron e, (0112) 

 observed by the latter. 



Measurements were obtained from the dominant rhombo- 

 hedrons from which a satisfactory axial ratio could be calcu- 

 lated. 



