Rogers. | Minerals of the Galena-Joplin District. — 461 
some calcite crystals has been proven to be zinc sulphide in- 
stead of cadmium sulphide, as had long been thought. Yet 
the fact remains that greenockite does occur, but, perhaps, in 
smaller quantities than is generally believed. It is not suf- 
ficient to call every yellow coating greenockite. 
W urtzite. 
Composition, zine sulphide, ZnS; zinc =67 %, sulphur = 33 %; hardness, 
3-5-4; gravity, 3-98; color, brownish black; crystallization, hexagonal sys- 
tem. 
Observed forms: 0/0001!0P; m{1010} oP; 1{5051!5P. 
Wurtzite occurs as small hemimorphic crystals, averaging 
about two mm. in length and one mm. in thickness in cavities 
in massive zinc sulphide (wurtzite?). One end of the crystal 
is terminated by the basal plane (pedion), while the other 
end, which is usually the one attached to the matrix, is ter- 
minated by the pyramid, 1 {5051} 5P, a recent form for 
wurtzite given by Souheur.® Occasionally, however, the 
basal plane is observed on this end (complementary pedion) , 
as is also a lower pyramid, the symbol of which cannot be de- 
termined on account of its small size. Figures 13, 14 and 15 
represent the combinations observed. On account of the 
small size of the crystals and the dull surface of their faces 
they could be measured neither with the contact nor with the 
reflection goniometer. Measurements were accordingly made 
under the cross-hairs of a petrographic microscope, and are 
as follows: 
nae a Average. Calculated. 
cal 0001,5051 12 measurements, 11° 55’ 11° 57’ 
1,l™ 5051 ,5051 11 «6 65° 317 66° 67 
The unit prism m frequently occurs, and often the pyr- 
amid and prism are in oscillatory combination. Parallel 
ageregates are common, consisting of two or more crystals 
built upon each other, their vertical axes coinciding. At the 
free end of a crystal two or more subindividuals are present 
side by side, their lateral axes coinciding. No observations 
bearing upon the rhombohedral character of wurtzite could 
be made, owing to the small size of the crystals. 
8. Souheur: Zeit. f. Kryst. u. Min., vol. 23, p. 549, 1894. 
31—viii 
