Dana and Wells — Selenium and Tellurium minerals. 79 



selenium and tellurium was effected by the very convenient 

 method of Divers and Shimose.* In carrying out this method, 

 it was found that the selenium obtained by a single separation 

 sometimes contained quite a large quantity of tellurium, but 

 the latter could be readily removed by one or two repetitions 

 of the process. 



The results obtained are as follows, after deducting 65 -68 

 per cent of gangue consisting of about 43 per cent of silica 

 and 19 per cent of barite with a little gypsum and a trace of 

 alumina : 



Se .... 29-31 



Te 70-69 



100-00 



The mineral is, therefore, intermediate between selenium and 

 tellurium in composition, and contains these elements in very 

 nearly the ratio of 2 : 3 ; though we do not attach any importance 

 to the ratio, for the mineral obviously represents simply an 

 isomorphous mixture of these two elements. It is of great 

 interest, however, since it is the nearest approach to native 

 selenium which has yet been found in nature. f The mineral 

 most closely allied to it is a native tellurium from Faczebaja 

 in which Foullon found 6'7 per cent of selenium. It seems to 

 us, therefore, to deserve to be given a somewhat prominent 

 position and we propose to call it Selen-tellurium. It is inter- 

 esting to note here the recent observations of Muthmann^; 

 showing among other new points the existence of an allotropic 

 form of metallic selenium in hexagonal-rhombohedral crystals, 

 closely isomorphous with metallic tellurium. Our mineral is 

 shown by its hexagonal cleavage to belong with these, as was 

 to have been expected. 



Associated with the selen-tellurium are a few minute trans- 

 parent crystals having a pale yellow color and adamantine 

 luster, which have the appearance of tellurite. The quantity 

 is so extremely small as to make an examination unsatisfactory 

 and we defer the matter in the hope of obtaining additional 

 material. 



Quite distinct from the yellow crystals just mentioned, is a 

 greenish yellow mineral which is also obviously an oxidation 

 product and which is present more abundantly. It is best shown 

 in two or three specimens, having the aspect of a quartzose con- 

 glomerate and containing patches of a grayish metallic mineral 

 which proved to be nearly pure tellurium. Through this it is 



* Jour. Chem. Soc, xlvii, 439. 



f We pass over Del Rio's unconfirmed statement, in regard to the occurrence 

 of native selenium in Mexico, as not deserving of serious consideration. 

 % Zeitschr. fur Kryst, xvii, 356, 1890. 



