Hillebrand and Penfield — The Alunite-Jarosite Groujp. 211 



Art. XXY. — Some Additions to the Alunite-Jarosite Grouy 

 of Minerals ; by W. F. Hillebkand and S. L. Penfield. 



Concerning two new varieties of jarosite which will be 

 described in the present communication, one is from l^evada, 

 and was collected by Mr. H. W. Tnrner of the United States 

 Geological Survey and sent to the survey laboratory at Wash- 

 ington for identification ; the other is from Nev/ Mexico, and 

 was sent by Mr. J. H, Porter of Denver, Colorado, to the 

 Mineralogical Laboratory of the Sheffield Scientific School. 

 Except for slight differences in color the two minerals look 

 exactly alike, each consisting of minute, isolated, tabular crys- 

 tals, which, as may be seen with the microscope, consist of com- 

 binations of a rhombohedron with largely developed basal 

 planes. By chance it happened that the present writers dis- 

 covered that they were both engaged in the investigation of 

 compounds belonging evidently to the same group, and it was 

 decided to bring the results together into one paper. 



Natrojavosite. 

 The material collected by Mr. Turner was obtained on the 

 east side of Soda Springs Yalley, ]N"evada, on the road from 

 Sodaville to the \^ulcan Copper 

 Mine. It consists of a glistening 

 powder, made up of perfect crystals 

 having the habit shown in figure 1, 

 although generally only one rhom- 

 bohedron, r, is present instead of 

 two, as shown in the figure. The 

 largest crystals observed were 0'15°'" 

 wide and 0-025"^"^ thick, and the 

 general average would not be over 

 half that size. In spite of being so 

 minute, however, it was possible to 

 measure the angles of the crystals 

 with the reflection goniometer, the 

 chief difficulty arising not so much 

 from their small size as from the 

 vicinal character of the basal planes. 

 After repeated trials a crystal was 

 found having a fairly good basal 

 plane, and from this crystal the following angles were obtained : 



Measured. 

 ^1011=51° 53'* 



C/sr, 0001 



C/s/, 0001a1101=51 



53 



C/^t\ 0001/s0111=52 26 



Calcu- 

 Measnred, lated. 



C/vS, 0001 ^0221^:68° 42' 68° 35' 

 C/vs', 000l/^2021=:68 48 '' " 

 r/sr', 101L/sll01 = 86 5 85 54 



Am. Jour. Scl 

 15 



-Fourth Series, Vol. XIY, No. 81. — September, 1902. 



