AKT. 13 



MINERALS FROM SOUTHERN UTAH — SHANNON 



Analysis and ratios of ammoniojarosite 



(Earl V. Shannon, analyst) 



Except in that the water content is a little low the results agree 

 very well with the formula 



(NH J 20.3Fe,03.4S03.6H,0. 



The existence of the ammonia member of the group is thus estab- 

 lished. The theoretical composition to satisfy the above formula is : 

 (NHJ2O.5.43; Fe,03 49.92, SO3 33.38, and H.O 11.27 per cent. 



Under the microscope the analyzed sample was found to be made 

 up of minute transparent tabular grains, a few of which showed 

 hexagonal outline. These were too small to yield an interference 

 figure, but those lying on the basal plane are dark between crossed 

 nicols, so the mineral is uniaxial or nearly so. Plates on edge show 

 positive elongation, so the mineral is probably optically negative. 

 The refractive indices could not be accurately measured but they are 

 approximately^ «)= 1.800, e= 1.750 both ±0.005. The ammoniojarosite 

 has probably been formed through the oxidation of pj'^rite in the 

 liffnitic material. 



One lot of material, when received, consisted of long-fibrous masses 

 and shorter fibers having a pearly or silky luster. This gave the 

 qualitative reactions of epsomite. The only impurity in this mate- 

 rial was a little bentonite, and fragments of the epsomite occur in 

 another sample of the bentonite, indicating that the magnesium 

 sulphate occurs associated with the bentonitic clay and not in the 

 lignite which carries the tschermigite and ammoniojarosite. When 

 received tliis fibrous epsomite was lustrous and firm. Microscopic 

 examination was fortunately made immediately after the samples 

 were received before any dehydration hud begun. The mineral was 

 biaxial and negative with 2E medium small. The grains are lath- 

 shapod and showed parallel extinction. They lie on either one of 



