Hillebrand — Analyses of Tysonite, etc. 51 



Art. YII. — Miner alogical Notes : Analyses of Tysonite, 

 .Bastnasite, Prosopite, Jeffersonite, Oovellite, etc. ; by W. 

 F. Hillebrand. 



Lsr the following pages are given the results of several 

 analyses of minerals made in the laboratory of the U. S. Geo- 

 logical Survey during the past few years. In the cases of 

 tysonite and bastnasite the results show that the formulas 

 attributed to them are correct, which in the absence of fluorine 

 determinations could not hitherto be affirmed. In the other 

 cases the analyses are interesting only as affording additional 

 data regarding rare minerals from new localities. 



Tysonite and Bastnasite. 



These minerals formed a single fine specimen half as large as 

 the fist, without crystal faces, from Cheyenne Mountain, near 

 Pike's Peak, Colorado. The bastnasite covered one side of the 

 tysonite to the depth of an inch. The line of demarcation 

 between the two minerals was sharp, but examination of their 

 sections by Mr. H. W. Turner showed the tysonite to be per- 

 meated by stringers of bastnasite along numerous cracks and 

 that occasional grains of the latter were imbedded in the 

 tysonite, which accounts for the C0 2 shown in the tysonite 

 analysis. Attached to the tysonite at portions of its surface 

 were other white and brownish alteration products derived 

 from it, as shown by qualitative tests. The tysonite was evi- 

 dently the remnant of a single large crystal, since, according 

 to Mr. Turner, all parts had the same optical orientation. Mr. 

 Turner further found the optical properties of both minerals, 

 so far as determinable, to agree with those given in Dana's 

 Mineralogy, and the index of refraction of the bastnasite to be 

 greater than that of the tysonite. He likewise noted in both 

 minerals minute colored inclusions, indeterminable and very 

 trifling in amount, and also in the tysonite " numerous minute 

 angular cavities in which there is a liquid, often with gas 

 bubble. Minute, clear, cuboidal crystals, apparently isometric, 

 were also noted in some of these cavities." 



The composition of the minerals was found to be as given by 

 Allen and Comstock, with the exception that the ratios 

 of cerium oxide to the oxides of the lanthanum group are not 

 quite the same. The formulas are not thereby affected. 



Cerium was separated from the lanthanum group oxides by 

 two precipitations by potassium hydroxide followed by long 

 introduction of chlorine. After recovery of the earths remain- 

 ing in solution, they were again subjected to this treatment to 

 be certain of having all the cerium. In one case a small por- 

 tion was thus recovered. The cerium was most carefully 

 examined for thorium and traces of what appeared to be thoria 



