362 \\ . T. Sohaller — The Alun He- Bendantite Group. 



by Slavik,* who described jarosite from Schlaggenwald which, 

 in basal section, showed a division into six parts, each part 

 being biaxial, with the trace of the axial plane normal to the 

 prism edge. The negative, biaxial interference figure varied 

 in size in different crystals, up to 32°. Some basal plates were 

 pleochroic and decidedly doubly refracting. 



Hamlinitef from" Switzerland, at first thought to be a new 

 species and called bowmanite, shows:}: optical anomalies. The 

 larger crystals show a division into six sections, each showing 

 a positive, biaxial figure, 2E varying from 0° to 50°. Hinsdal- 

 ite likewise shows a pseudohexagonal character,^ the crystals 

 being built up of six sectors, each normal to an acute bisectrix, 

 2E varying from 0° to 40°. These optical anomalies are very 

 suggestive of dimorphism in the series. 



The isomorphous relation of sulphate and phosphate is istill 

 further confirmed by the presence of 2 - 72 per cent P a 6 in an 

 analysis of carphosiderite from France and also by the pres- 

 ence of nearly one per cent P 2 6 in a sample of alunite from 

 Utah, tested by the writer. 



The formula of bendantite and corkite have been taken as 

 suggested by LacroixJ namely the arsenate called bendantite 

 and the phosphate corkite. The composition of miriquidite, 

 munkforssite, and munkrudite are too little known to definitely 

 include them in this group, although their qualitative compo- 

 sition is such as to suggest their belonging here. 



Pharmacosiderite has been shown^ to contain considerable 

 potash and Hartley's formula 2FeAs0 4 .Fe[0(H,K)],.5H > can 

 be written analogous to that of hamlinite, as 2(H,K) 2 0.3Fe 2 3 .- 

 2As 2 6 .7H 2 + 4H 2 0, in which the 4H 2 does not really belong 

 to the mineral. Though pharmacosiderite is considered isomet- 

 ric, the form is very close to the rhombohedral crystals of this 

 group and it would be highly desirable to test the mineral 

 optically to see if it could be referred to a uniaxial mineral, as 

 it commonly shows weak double refraction. 



The composition of plumbogummite still needs careful study 

 and it is entirely possible that more than one species is included 

 under that name. The analyses of Hartley have established 

 the presence in quantity of C0 2 in some varieties, while the 

 analyses of Brazilian plumbogummite, given by Hussak, are 



*Slavik, Franz, Mineralcgisehe Notizen. Zeitsehr. Kryst., vol. xxxix, p. 

 297, 1904. 



f The name hamlinite is retained until its identity with or distinction from 

 goyazite is definitely determined. 



% Bowman, H. L., On hamlinite from Binnenthal, Switzerland. Mineral. 

 Mag., vol. xiv, p. 389, 1907. 



§ See paper on Hinsdalite, this Journal, page 251, Oct., 1911. 



|Lacroix, A., Mineralogie de la France, vol. iv, p. 592, 1910. 



TJ Hartley, E. G. J., On the constitution of the natural arsenates and 

 phosphates. Mineral. Mag., vol. xii, page 152, 1899. 



