Dana and Wells — Selenium and Telhirium minerals. 81 



rates it widely from the Honduras ferric tellurite. Emmonsite 

 corresponds in composition more closely, being also a ferric 

 tellurite, and we were inclined at first to think that the two 

 minerals might be identical. Through the kindness of Dr. 

 Hillebrand we have had an opportunity to inspect the original 

 emmonsite, and furthermore Dr. Hillebrand has made a new 

 chemical examination of the scanty amount of material at 

 hand, the results of which are appended to our paper. Our 

 own examination did not extend beyond a microscopic study 

 of the cleavage plates, but these while confirming the points 

 made by Mr. Cross in regard to the cleavages and chief optical 

 characters, proved that in appearance the Honduras mineral 

 and emmonsite are widely different. Moreover, Dr. Hille- 

 brand's recent results show that the two minerals differ both 

 in ratio of tellurium to iron, and also in amount of water. 

 The Honduras mineral consequently cannot be united with 

 either of the minerals named, and although our knowledge of 

 its physical characters is imperfect, the simplicity and exact- 

 ness of the chemical formula shows that it deserves to rank as 

 a definite mineral species. We propose, therefore, to call it 

 Durdenite after the gentleman to whose kindness we are 

 indebted for all the material we have had to use. 



Note on Emmonsite by Dr. W. F. Hillebrand. 



I have attempted a re-analysis of emmonsite with the extremely 

 limited quantity belonging to Mr. Cross, which he kindly con- 

 sented to sacrifice for the purpose. Unfortunately the analysis 

 was not entirely successful, but what was done upholds the cor- 

 rectness of my former analysis and seems to prove that the two 

 niinerals are distinct. The weight taken for analysis was •0V64 

 grams. The water was determined in this by heating in a boat 

 with a plug of dry sodium carbonate filling the tube in front, and 

 collecting the water in a calcium chloride tube. The weight 

 found was *0032 grams, or 4*2 per cent. This, under the circum- 

 stances, is as near as could be expected to my original deter- 

 mination (3"28 per cent), which was made on less pure material, 

 and shows that emmonsite is distinct from the Honduras mineral, 

 which has over 10 per cent of water. After dissolving the 

 ignited mineral, a rather considerable portion of the solution 

 was unfortunately lost, but the relation of the iron and tellurium 

 in what remained was estimated ; the result being Fe 2 : Te = 

 1:3*75. This is very near that originally found, i. e., 1:3-65. 

 I did not detect any zinc in this analysis, which is confirmatory 

 of the opinion formerly expressed that it was present as an 

 admixture in some form. 



In regard to the behavior of emmonsite on heating it may be 

 added that even at as low a temperature as 100° C. it becomes 



Am. Jour. Sci. — Third Series, Vol. XL, No. 235. — July, 1890. 

 . 6 



