Q 



66 CALIFORNIA ACADEMY OF SCIENCES. 



forms project from the walls freely across the center of the cav- 

 ity; each needle carries two or three minute but perfect tabular 

 crystals of albite pierced directly through the center of the table. 

 The needles are at times quite straight, but more commonly 

 gently curved, spirally twisted, or bent sharply about. Some of 

 the larger needles split up at one end into two smaller ones, or 

 again into long brush-like subdivisions. 



One of the larger needles was detached and roasted, giving 

 copious sulphur fumes, and leaving a reddish-brown powder that 

 gave the characteristic iron reactions with borax and microcosmic 

 salt on platinum wire. The needles at once call to mind the 

 curiously distorted crystals described by Carl Vrba from Lill- 

 schacht in Przibram. [Note. — Zeitschrift der Krystallographie 

 for 1880. Bd. IV. p. 357. ] 



The exact crystallographic nature of the needles was at first 



somewhat of a puzzle. I finally ucceeded in finding one that 



promised results with the goniometer. It was' mounted on the 



large Fuess-Babinet instrument with two telescopes, belonging 



to the Museum of the University, and the following readings 



were obtained: 



a 1 214° 10' fair; bright. 



6 1 180° 30' good; very faint. 



c a 94° 20' good; bright. 



a 1 31° 10' good; very faint. 



d 1 345° 30' good; very faint. 



c 1 333 J 51' good; bright. 



The cross section of the needle was plotted in accordance with 

 these readings with the result given greatly enlarged in Fig. 10\ 

 It is at once seen from the above readings that a 1 and a 1 are the 

 only parallel faces on the needle. Inserting parallels to each of 

 the other faces into the cross-section and adding to the preceding 

 readings, the following which would have been obtained had 

 these faces been present: 



d 1 165° 30' 

 c 1 153° 51' 

 6i 1° 0' 

 c 2 274° 20' 



