28 



S. L. Penfield — Pearceite, etc. 



tions in basisity. The axes and angles have been taken from 

 the sixth edition of Dana's Mineralogy, with the exception of 

 those of xanthoconite and pyrostilpnite, which are taken from 

 Miers,* and of jordanite, taken from Baumhauer."^* 



ii 

















Change 



W 1 



ii 















C^pOT 



of axes 



Name. 



Composition. 



Syst. 



a : 6: c 



/? 



m/^m' 



equiv- 



from 



ilii 

















alent. 



Dana's 

 position. 





Chalcocite 



CuaS 



l-ns : 1:1-666 



60° 25' 



62° 35' 



a=h 



ii 1 



Pearceite 



9 AgsS . AS3S3 



M 



1-731 



1: 1-620 



89° 51' 



60 2 



61 49 







Polybasite 



OAgsS.SbaSg 



M 



vn\ : 



1: 1-580 



90 00 



60 2 



61 16 





IN 



Stephanite 



SAgaS.SbaSa 







1-589 



1:1-633 





64 21 



62 37 



a^b.^c 



C: 



Geocronite 



5PbS.SboS3 • 







1-723 



1:1-732 





60 16 





a=b.2c 





Jordanite 



4PbS.As2S3 



M 



1-862 : 



1: 1-883 



90 33f 



56 30 



65 01 



b=c.ic 





Meneghinite 



4PbS.Sb2S3 







1-891 



1 : 1-831 





55 45 





a=b.2U 





Proustite 



SAgaS . AS0S3 



R 



1-732 



1: 1-608 





60 



6l41i 



2c 



ill 



Pyrargyrite 



SAgsiS.SbsSa 



R 



1-732 



1:1-578 





60 



61 15 



2c 



' 



Xanthoconite 



SAgsS. AS2S3 



M 



1-919 



: 1:1-523 



88 47 



55 4 





|c 



\\ 



Pyrostilpnite 



SAg^S.SbsSg 



M 



1-946 



:1: 1-646 



90 00 



53 21 





|c 



h 



Bournonite 



3(Pb, Cu2)S . SbaSs 







1-875 



:1: 1-793 



/-/= 



56 8 



63 48 



2a. 2c 





Freieslebeuite 



5(Pb,Ag2)S.2Sb2S3 



M 



1-703 



1: 1-580 



92n4f 



60 48 





a=b. 





Dufrenoysite 



2PbS. AS2S3 







1-531 



:1: 1-876 



i A. {'=■ 



66 18 





a=c.2c 



nil 1 



Jamesonite 



2PbS.Sb2S3 







? 



: 1: 1-830 









a=G.2c 







Sartorite 



PbS, AS2S3 







1-856 



:1: 1-722 





66 38 





a=b.^c 



iii i 



Zinkenite 



PbS . SbsSs 







1-794 



: 1:1-709 





58 17 





a=b .|c 



M = Monoclinic. = orthorhombic. R = rhombohedral. 



In the majority of cases in the above table the change from 

 the position given in Dana has been made by a simple inter- 

 change of the a and h axes and by multiplying the vertical 

 axis in its new relation by a simple factor. The isomor- 

 phous relations of jordanite and meneghinite, studied by 

 Miers,:}: Krenner,§ Schmidt || and Groth^f are not at all clear. 

 The factor 2f given for the vertical axis is a rather unnatural 

 one, which if adopted would give to the forms observed on 

 meneghinite very complicated indices. The axial ratio sug- 

 gested by Schmidt, a:h:G = 0-4:862 : 1 : 1'8465, would give by 

 interchange of a and h and using the factor f for the vertical 

 axis ^:5:c = 2-0568: 1:1-8984 and m^m = 61° 62', values 

 which show the widest variations of any in the table from poly- 

 basite. It will be noticed that the vertical axes of the arsenical 



* Min. Mag., x, p. 185, 1893. 

 ** Sitz. Ber. Akad. d. Wiss., Berlin, 1891, p. 697. 



f Owing to the change of position of the axes, the inclination for jordanite 

 becomes 7 instead of /3 and for freieslebenite a instead of [3. 

 X Min. Mag., v, p. 325, 1884. 

 §Foldt. Kozl., xiii, p. 297, 1883. 

 II Zeitschr. Kryst., viii, p 613, 1883. 

 ^ Tabellarische Uebersicht, p. 33, 1889. 



