296 E. 11. jS. Bailey — Halotrichite from Colorado. 



Art. XXXIII. — On Halotrichite or Feather Alum, from 

 Pitkin County, Colorado ;* by E. H. S. Bailey. 



A FEW months since a sample of a mineral was sent by 

 J. J. Crippan, Esq., of Denver, Col, to the Laboratory of the 

 State University for identification. He stated that it came 

 from the Elk mountain range, and was found beside a ledge 

 of "black iron ore." As no record can be found of the 

 description or analysis of this mineral from an American lo- 

 cality, it has been thought that an investigation would be of 

 value. The mineral is quite soft, has a white color, and a 

 beautiful silky luster, resembling that of satin spar. Under 

 the microscope and, to a certain extent, by unaided vision, the 

 mineral appears to consist of capillary crystals arranged in par- 

 allel bundles. In some places the crystals, when viewed from 

 the end, are of a green or copperas color. Under the micro- 

 scope there appear to be attached to some of the fibers minute 

 black particles. In picking the mineral for analysis these 

 specks were eliminated as far as possible. There is only a 

 slight tendency towards oxidation on the surface ; and where 

 this occurs the mineral is yellowish red. 



The mineral is nearly all readily soluble in water and has a 

 slightly acid, and very astringent taste. It fuses easily in the 

 flame of a candle in its water of crystallization, and as the 

 temperature increases it boils and finally leaves a reddish mass. 

 If, however, the mineral be heated very gradually in a paraffin 

 bath it does not melt or lose its form, but gradually loses its 

 water. Afterwards, if heated nearly to redness, it retains ita 

 form, but gradually changes to a red color. 



As it was noticed that much of the water was given off at a 

 very low temperature, a quantity of the mineral was heated 

 below 100° C, and, in fact, till just before the close of the 

 experiment, below 85°, and the water thus driven off was 

 collected in a calcium chloride tube and weighed. The mass 

 was thus heated till no more water was given off at this tem- 

 perature. 33 '10 per cent of water was thus eliminated. The 

 remainder of the water was driven oil at a much higher tem- 

 perature ; very little, in fact, going off below 250° C. 



As the mineral was not completely soluble in water and 

 hydrochloric acid, the solution was evaporated to dryness and 

 silica separated as usual. This silica, or an insoluble silicate, 

 is probably not a proper constituent of the mineral, but so 

 closely associated with it that even in the cleanest and most 

 silky fibers it cannot be separated mechanically. The blow- 

 pipe reactions for iron are obtained. If the silky fibers be 



* Read before the Kansas Acad, of Science. 



