Hydrous Silicate of Manganese and Calcium. 503 



little variation wliicli can be ascribed to the dust-like 

 material and it seems probable that, despite its conspic- 

 uous appearance under the microscope, this is exceed- 

 ingly tenuous and of practically negligible mass. It is 

 believed that no appreciable amount of extraneous 

 manganese oxide was included in any of the samples 

 analyzed. 



The results obtained upon analysis of the three separate 

 samples are given in the following table. Standard 

 analytical methods were used; the state of oxidation of 

 the manganese was determined by collecting, in potassium 

 iodide solution, the chlorine evolved upon solution of the 

 mineral in hydrochloric acid and titrating the liberated 

 iodine with standard sodium thiosulphate solution. 



Analyses of crystalline orientite. 



Constituent 12 3 Average 



Si02 32.97 31.42 33.05 32.48 



AI2O3 2.05 1.03 .17 1.08 



Fe203 1.36 1.62 1.70 1.56 



MnO 29.93 28.60 31.22 29.92 



3.39 3.24 3.21 3.27 



CaO 22.04 21.90 23.47 22.47 



MgO trace trace trace trace 



ZnO trace .... .... trace 



H.,0 — 110°C 03 .... .04 .03 



H.O + 110°C. . . . 8.48 .... 7.39 7.93 



CI trace .... trace 



Total 100.25 100.25 98.74 



The excess^ of oxygen shown in each analysis indicates 

 that essentially all of the manganese is in the manganic 

 state; the average column of the above table with the 

 excess oxygen united with an equivalent amount of MnO 

 to form MusOg yields ratios as follows : 



Ratios of orientite. 



SiOo 5386 53.86 1.02x5 



ALO3 0108] 



Fe.Og 0098 i^ 22.48 1.05 x 2 



Mn,03 2044J 



MnO 0130) 41.36 .97 x 4 



CaO .4006) 



H2O .- 4402 44.02 1.04 x 4 



