34 
CONTRIBUTIONS TO MINERALOGY. 
[bull. 26: 
The ratio of Fe 2 O a : Na 2 : S0 3 : H 2 is evidently 3:1:4:6 as in 
ordinary jarosite, where the alkali is potash instead of soda. The 
slight excess of Fe 2 C> 3 and H 2 0, as indicated by the ratio, is evidently 
due to some ferric hydroxide; probably the dark ferruginous impuri- 
ties seen under the microscope are in part responsible for this, and 
there are also traces of some arsenate and silicate present. By attrib- 
uting the excess of Fe 2 3 and H 2 to impurities, it is found that 94 pel 
cent of the material analyzed may be regarded as pure natrojarosite! 
as indicated below: 
FeA 
Na 2 
K 2 0. 
SO,.. 
H,0. 
After deducting impuri- 
ties. 
46. 43 or 49.39 
5. 81 or 6.18 
. 35 or . 37 
30. 96 or 32.94 
10. 45 or 11. 12 
94. 00 or 100. 00 
Theory for 
Na.,Fe fi [OH]! 
[S0 4 ] 4 . 
49. 4ii 
6. m 
32. 9£ 
11. B 
100. 0( 
That 6 per cent of impurities should be present in a crystalline 
powder such as was analyzed is not surprising when it is taken ink 
consideration that it would require something like 2,500,000 crystal:! 
to make one gram of material, the estimation being based on tin 
assumption that the crystals are 0.10 mm. in axial diameter and 0.0' 
mm. thick, Avhich is certainly above their average size. 
Among the specimens from Cooks Peak, New Mexico, sent to th< 
Sheffield laboratory by Mr. Porter, were some masses of a rathe 
firmly cemented aggregate of minute crystals of a mineral of the jarc 
site group. The specimens are of a brownish-yellow color, and hav 
in places the glistening appearance of a mica-schist. They also loo > 
as though they had been subjected to pressure and had been some 
what sheared. The material is rather easily crushed, and the powdei 
when examined Avith the microscope, exhibits the proprieties of th? 
natrojarosite just described. The crystals are associated with a litth 
limonite and quartz, and pure material for analysis could not b 
obtained. Only a partial analysis, therefore, was undertaken wit 
the following results: 
Fe 2 3 55.60 
Na 2 4. 49 
K 2 77 
PbO 96 
S0 3 and H 2 were present but not determined. The results are sui 
cient to indicate that the material is essentially natrojarosite. 
