Palache and Wood — Crystallographic Study of Miller ite. 343 



Art. XXXVII. — A Crystallographic Shcdy of Millerite • by 

 Charles Palache and H. O. Wood. 



The crystallographic character of millerite was first defined 

 by Miller in 1835 in a paper* interesting historically as con- 

 taining the first presentation of his index system_of notation. 

 He determined the forms o, (0001), b, (1010), k, (2130), e, (0112), 

 r, (1011), r 19 (0111) and v, (5052) on crystals without natural 

 terminations, but which had been broken across. And on a 

 single_ terminated crystal with dull faces, he found the form 

 t, (0331) by contact measurement. The angle o^r = 20° 50' 

 was the average of several readings, and led to the axial ratio 

 a : c = 1 : 0*3295 which is at present accepted. In the lack of 

 details as to faces and measurements, we are forced to conclude 

 tlrat he, at that time, considered five kinds of cleavage present, 

 parallel to o, e, r, /•„ and v. In his Mineralogyf the matter 

 is presented somewhat differently. The prism #, (1120) is 

 added, and instead of v, (5052), is given e^ (1012), without 

 explanation. He also states that possibly the appearance of 

 cleavage on both positive and negative rhomboheclrons, r and 

 7\ and e and e^ is due to concealed twinning on_the vertical 

 axis. The occurrence of the rhombohedron v, (5052), is there- 

 fore left in doubt, and cleavage parallel to the base and to the 

 two rhombohedrons r and e is indicated. 



In 1892, Laspeyres^: described beyrichite and paramorphs of 

 millerite after beyrichite. He concludes that all millerite is 

 derived from beyrichite, and that for the crystals of both 

 minerals examined, the crystallographic characters are identi- 

 cal. The forms observed were "5, (1010), a, (1120), i, (4lo0), 

 r, (1011) and <?, (0112); the two last both as cleavages and as 

 dull terminal faces, and each in apparently positive and nega- 

 tive positions through twinning about the vertical axis. The 

 axial ratio a : c = 1 : 0*3277 was derived from measurement of 

 the cleavage rhombohedron. 



The form i, (4150), is based on poor measurements, the 

 average differing by more than a degree from the calculated 

 value, and therefore is to be regarded as very doubtful. 



In 1893, the same author in a paper§ on the various nickel 

 deposits of the Rhine, describes various occurrences of miller- 

 ite. On specimens from two localities, terminated but not 

 measurable crystals were observed, on which c, (0001) and r, 

 (1011) were present together with the ordinary prism forms. 



The list of forms known on millerite up to the present time 



* Phil. Mag., vi. 104, 1835. \ Phillips Mineralogy, 163, 1852. 



% Zeitschr. f. Kryst., xx, 535, 1892. 



g Das Vorkominen tmd die Verbreittmg des Nickels im Eheinischen Schie- 

 fergebirge. Verb. Nat. -hist. Ver. Eheinl., 1, 142, 1893. 



