Geology and Natural History. 439 



would make the species tetrahedral like boracite, but this we cannot 

 however assert positively on account of the present rarity of the 

 mineral. Besides these faces of the octahedron (or tetrahedron) 

 we have also observed the cube modifying the rhombic-dodecahe- 

 dron. One very perfect crystal contained an irregular cavity 

 full of a liquid in which was a moving bubble of air (or gas.) 

 It also showed, by transmitted light, numerous lines of growth 

 parallel to all the planes. 



On the composition of the Fayalite from Cheyenne 3ft., Colo- 

 rado* — This mineral has the high specific gravity of 4-35, shows 

 cleavage, (imperfect) at right angles in two directions, is fusible 

 and gelantinizes with acids. It occurred in this instance as a 

 mass weighing nearly ten pounds and was quite abundant in the 

 vicinity in the granite. Analysis leaves no doubt as to its nature. 

 The results were: 



1. 2. 



Si0 27'30 27.66 



FeO 5-83 65-794 



MnO .._. 4-17 



CaO 0-47 



98-24 



The iron may be present in both the ferrous and ferric state 

 but this point was not determined, or the reasons for the loss 

 ascertained. 



13. 3fineraloc/ical Notes ; by W. E. Hidden, (communicated.) 

 — Remarkable discovery of Bastnaesite and Tysonite. — In the 

 summer of 1889, Mr. J. G-. Hiestand, of Manitou Springs, Colorado, 

 brought to my attention and sent samples of a new discovery of 

 bastnaesite and tysonite, which he had made in the Pike's Peak 

 region, at no very great distance from Maniton. He reports that 

 the total quantity found weighed over six kilograms and was 

 originally all included in one great group or mass. Hexagonal 

 tabular crystals, somewhat modified, nearly two inches across, of 

 a clear deep brown color, made up the exterior layers of the 

 larger fragments while the interior and greater portion was com- 

 posed of the wax-yellow unaltered tysonite, in parts perfectly 

 transparent. The specific gravity of several fragments was found 

 to be only 6.007. For novelty's sake a gem was cut that weighed 

 two-thirds of a gram, but it did not have very much brilliancy. 

 Some sections were made for optical examination and have been 

 sent to Prof. Penfield for that purpose. 



A white mineral of an earthy nature and seemingly a product 

 of alteration occurs in the bastnaesite and tysonite in large 

 patches. Its specific gravity = 4-145. It lost 21-02 per cent 

 after being strongly ignited and was then wholly soluble in 

 HN0 2 making a deep red solution, (Ce). It may prove to be a 

 mixture of bastnaesite with lanthanite. 



* See this Journal, March, 1885, p. 250. 

 Am. Jour. Sci.— Thtrp Series, Yol. XLI, No. 245.— Mat, 1891. 

 29 



