Gaylussite and Hanhsite frovi California. 131 



Three types of crystals have been observed, represented in 

 figs. 7, 8 and 9. The largest crystals, sometimes 20°^'° in 

 greatest diameter, are developed like fig. 7, but the faces are 

 generally rough. Crystals, with the habit shown in fig. 8, are 

 seldom over 10™°" in diameter. Only a few crystals of the 

 third type, fig. 9, were observed, and in order to show the 

 development of the faces to better advantage, the figure has 

 been drawn with the pinacoid, h 010, in front. It is only on 

 crystals of the latter type that the pinacoid 5, which is appar- 

 ently an unusual form on gaylussite, is developed. Although 

 many of the crystals are colorless and transparent, many are 

 cloudy, owing to impurities. 



The forms were identified by the following measurements, 

 the calculated angles being derived from the axial ratio estab- 

 lished by Phillips : * 



d\h\ ^— 1-4897: 1 : 1-4442; fi 



'78°26f' = 001 A 100. 



m A m 

 111 A e 

 e AS 

 e \r 



TAT 



r AS 



llOAlIO 



XYXCaOLUCU, 



111°8' 



vaiuujaieu 



lino' 



IIOaOII 



42°5^' 



42°21' 



Oil A oil 



109°34i' 



109''30' 



Oil A 112 



27°7 



2'7°44' 



Il2An2 



69°33' 



69°29' 



112 A 101 



39°49' 



40°21 



The measurements could not be made very accurately, as the 

 small crystals did not give very good reflections of the signal 

 on the goniometer, while the larger ones could only be meas- 

 ured with the contact goniometer. 



The specific gravity of some of the purest crystals, obtained 

 by means of the heavy solution, is 1*992. This is somewhat 

 higher than is usually given for this mineral. Phillips,f how- 

 ever, gives practically the same value, 1*990, for a remarkably 

 brilliant crystal upon which he made his crystallographic 

 determinations. 



Optical properties. — The principal work on the optical prop- 

 erties of this mineral is that by Des Cloizeaux:): who determined 

 the angle of extinction on the pinacoid d. 010, the apparent 



*Philos. Mag. i, p. 263, 1827. + Ibid., p. 265, 1827. 



X Ann. d. Mines, Y, xiv, p. 400, 1858. 



