524 Van Horn and Cook, — New Occurrence of Pearceiie. 



Physical Properties and Pyrog)iostics. 



The physical properties of the pearceite from the Veta Rica 

 mine are very similar to those from the Druinlummon mine, 

 Marysville, Montana, described by Penfield.* The mineral is 

 black, and has a splendent metallic luster. It has a very 

 pronounced conchoidal fracture, and is exceedingly brittle, 

 which accounts for the fact that not enough crystal faces 

 remained in the pyramid and prism zones to properly orientate 

 the mineral and accurately determine the new twinning law. 

 A specific gravity of 6'067 was obtained from the average 

 of four determinations on two different crystals, in which the 

 separate results were 6-01, 6'10, 6 - 02, and 6-14. A fifth 

 result obtained was 6"33, which the writer feels is not accu- 

 rate. However, if the average of all five were taken, the maxi- 

 mum specific gravity possible would be 6'12. 



Although the streak is black, and the mineral is practically 

 opaque, nevertheless if very small pieces are observed with a 

 high power objective in convergent light, a brownish green 

 color is apparent on the edges. No change of color is percept- 

 ible if the mineral is rotated between crossed nicol prisms. 



In a closed tube in the flame of a spirit lamp, the mineral 

 decrepitates, fuses easily to a black globule, and deposits a 

 white crystalline sublimate consisting of octahedrons of As 2 3 . 

 The globule when heated with the blowpipe gives a yellow 

 sublimate of As 2 S 3 . In the open tube it gives a sulphurous odor, 

 and a white crystalline coating of As,0 3 . On charcoal, the 

 mineral gives a faint white coating of As 2 3 and the odor of 

 S0 2 . After continued blowing, a malleable bead is obtained. 

 If this is treated with borax on platinum wire, it alloys with 

 the wire but gives a bead which is green while hot but blue 

 when cold, indicating copper. Continued fusion of the alloyed 

 wire gave a bead which was dark green when cold. 



Geological-Mineralogical Laboratory, 



Case School of Applied Science, Cleveland, Ohio, February, 1911. 



* Op. eit., page 23. 



