216 Hillehrand and Penfield — Additions to the 



per cent of impurities in such a crystalline product is not to be 

 wondered at. 



Jarosite and Alunite. 



As seen from the analyses of these minerals which have been 

 published, the alkali metal they contain is almost always potas- 

 sium, though sodium is at times present. The formulas assigned 

 to the two minerals are therefore K2C^ + 3Fe203+4S03+6H20 

 and K.O + SAIA + 4:803 + 6H,0, which may be variously 

 expressed, as will be indicated later. 



A mineral corresponding to natrojarosite of this article, 

 though containing a little potash, has been described by W. P. 

 Headden* from the Buxton mine, Lawrence Co., S. JD. The 

 crystals are described as scales, consisting of a combination of 

 base and rhombohedron. The material analyzed was evidently 

 somewhat impure, as quartz and some As^O^ are reported. As 

 the ASjOj evidently does not belong to jarosite, the assump- 

 tion may be made that some scorodite, FeAsO/2H20, is present, 

 and the results of ELeadden's analysis* may then be interpreted 

 as folio ws : 



Original Scorodite Natro- 



analysis. and quartz, jarosite. Eatio. 



Fe/)3 46-27 1-60 44-6'7 or oO'lO 3-13 



Na^O 4-35 4-35 '* 4-86) 



K^O 1-47 1-47 " 1-65 V 1-04 



CaO._ 0-39 0-39 " 0-44) 



SO3 ..28-46 28-46 " 31-93 4*00 



H,0 10-55 0-72 9-83 " 11-02 6*13 



As^O^.- 2-36 2-36 



Quartz 6*10 6-10 



99-95 10-78 89-17 100-00 



Thus, assuming the presence of 4*68 per cent of scorodite and 

 6*10 of quartz, and deducting them, the remainder agrees very 

 closely with natrojarosite, giving a good ratio, very near 

 3:1:4:6. 



Alunite 'containing considerable soda has been described by 

 W. Cross-f from Rosita Hills, Colorado, and by^ E. B. Hurl- 

 burtij: from Eed Mountain, Colorado, and analyses of both 

 minerals show about equal percentages of K^O and ISTa^O, or a 

 molecular ratio of ILfi : J^a^O = 4:7. The occurrence, there- 

 fore, of sodium in the jarosite-alunite group is in accordance 

 with previous observations, but the case is quite different with 

 lead. As far as the present writers are aware, this is the first 

 instance on record where lead has been observed isomorphous 

 with the alkali metals. It is interesting to note that the alunite 

 from Red Mountain, Colorado, occurs as a crystalline powder, 



* This Journal (3), xlvi, p. 24, 1893. f H^id- (3), xli, p. 472, 1891. 



tibid. (3), xlviii, p. 130, 1894. 



