80 Dana and Wells — Selenium and Tellurium minerals. 



scattered in points and narrow veins. It is soft, with, hardness 

 from 2 to 2-5 and is easily crushed to powder. The surface, 

 when exposed, is small mammillary and but little structure is 

 discernible even under the microscope, although a tendency to 

 separate into distinct scales is noted. The action on polarized 

 light is very feeble. The mineral is intimately mixed with 

 the gangue and it was only by using extreme care that it was 

 found possible to separate a sufficient quantity of material for 

 analysis, the purity of which could be regarded as beyond all 

 question. This was finally accomplished, however, and an 

 analysis made with the following results. Of the whole 

 amount obtained, viz : 0*32 grams, 0*12 gr. was taken for a 

 water determination and the remainder 0*20 gr. for the other 

 determinations. The results, considering the small quantities 

 used, are very satisfactory. The analysis is as follows : 



Water 7*67-5- 18=-426 



Te0 2 47-20-4-157 = -301 | 



Se0 2 1-60-4-111 = -014 f 



Fe 2 3 19-24-^-160 = -120 



Insol. 23-89 



3-55 





4-06 



4 



2-62 



or 



3-00 



or 3 



1-00 





1-14 



1 



99-60 



These ratios are not quite exact, but there can be no doubt 

 that it is a normal ferric tellurite of the composition Fe 2 3 . 

 3Te0 2 .4H 2 or Fe 2 (Te0 3 ) 3 +4H 2 0. The slight excess of 

 Fe 2 3 shown by the ratio very probably comes from the red- 

 dish ochreous material associated with it. 



The calculated composition, with -^ of the Te atoms replaced 

 by Se, is : 



Calculated for Analysis 



Fe 2 O s 2 7 tt Te0 2 -f- SeO s . 4H 2 0. Deducting Insol. Res. 



Te0 2 64-41 Te0 2 __ 62*34 



Se0 2 2-28 SeO„ 2-12 



Fe 2 3 22-97 Fe„0 3 25-41 



H o 10-34 HO 10-13 



100-00 100-00 



That the mineral is a ferric telhm'fe is evident since it gives 

 off no chlorine when boiled with HC1, nor does it give any reac- 

 tion for ferrous iron when dissolved in cold HC1. 



Two other tellurium-iron minerals have been thus far 

 described : these are Qj&a.\h?&* ferrotellurite and the emmonsite 

 of Hillebrand.-f- Our mineral is like ferrotellurite in color, 

 but, if the results of Genth's qualitative trial can be accepted 

 as conclusive, his mineral was a ferrous tellurate, which sepa- 



* Proc. Acad. Nat. Sci. Philad., xvii, 119, 1877. 

 f Proc. Colorado Sci. Soc, ii, 1885. 



