6 PROCEEDIISrGS OF THE NATIONAL MUSEUM vol.74 



monia over soda and potash. Consequently it has been given the 

 name ammoniojarosite. Thus five definite members of the jarosite 

 group are now known, having the following formulas: 



Jarosite, K^O, SFeiOs, 4SO3, 6H2O. 



Natrojarosite, NaiO, SFejOs, 4SO3, 6H.0. 

 Plumbojarosite, PbO, SFe^Oa, 4SO3, GH2O. 

 Argentojarosite, Ag:0, SPesOs, 4SO3, 6H2O. 

 Ammoniojarosite (NH.)20, 8Fe203, 4SO3, GH2O. 



These minerals form a division of the large alunite-beudantite series 

 of minerals as defined by Schaller ^° and numerous other related 

 compounds are to be expected. Ammoniojarosite and argentojaro- 

 site, the two newest members of the group, have their type localities 

 in Utah and all of the laiown members of the group have been found 

 in that State. 



The Utah ammoniojarosite forms small, soft, ocherous lumps of 

 pale yellow color and darker hard, irregular, flattened nodules up 

 to 4 centimeters broad by 5 millimeters thick, embedded in blackish- 

 brown lignitic material. Some of it is stained darker brown by limo- 

 nite and a little occurs in shaly masses largely composed of the im- 

 perfect Cretaceous fossils mentioned above. On fresh fracture the 

 color of most of the purer lumps is light ocherous yellow and the 

 luster is dull-waxy to earthy. 



One of the largest and purest lumps was selected and freed as far 

 as possible from adhering lignite. This was finely ground and di- 

 gested with frequent stirring in hot distilled water long enough to 

 remove all tschermigite and other water-soluble salts. It was then 

 filtered out of suspension, washed thoroughly with hot water, dried 

 in air, reground, and allowed to stabilize its water content in air for 

 several days. The powder was then analyzed by standard methods. 

 Five grams were weighed out, dissolved in hot hydrochloric acid and 

 filtered. The undissolved material was dried in air for several days 

 and then weighed, after which it was ignited and again weighed. 

 It consisted principally of lignite with a very little clayey material. 

 The solution was made up to 500 cc. and divided into 5 aliquot parts. 

 On these portions, equivalent to 1 gram of sample each, the con- 

 stituents other than water and ammonia were determined. Water 

 and ammonia were determined by standard methods on separate por- 

 tions of the same powder. The analysis gave the following results 

 and ratios : 



10 Waldemar T. Schaller. The ahinite-beudantitc group. U. S. Geol. Survey Bull. 509, 

 ■pp. 70-76, 1912. 



