so 3 



45-89 



COo 



5-42 



CI 



2-36 



Na 2 0* 



46-34 



134 W. R Hidden— On Hanlcsite. 



determination. The results of measurements confirmed my 

 first suspicions of their true hexagonal character, though only 

 approximate, being made with a hand goniometer. Since, 

 however, the hexagonal aspect of the mineral might possibly 

 be due to complex twinning of orthorhombic individuals, it 

 seemed advisable to have this question decided on the basis of 

 an optical examination. For this purpose three of the best 

 crystals were kindly given by Professor Hanks, and these 

 were sent by me to Dr. Edward S. Dana ; the crystals being 

 quite clear. In a few days he reported them to be normally 

 uniaxial with negative double refraction, and thus they were 

 positively proved to be different from thenardite. An analysis 

 being now necessary to settle the composition of the mineral, I 

 placed sufficient material in the hands of Mr. James B. Mack- 

 intosh, E. M., for that purpose, and he has very kindly done 

 the work, with the following results : 



Corresponding to 



Na 2 S0 4 81-45 



Na 2 C0 3 13-06 



NaCl 3-89 



Na 2 (excess) 1-08 



99-48 



These results give the following molecular ratios for 



Na 2 S0 4 57-3 "] ( 3-95 



Xa 2 C0 3 14-5 I J 1-00 



NaCl 6-65 f or ] -46 



Na 2 1-75 J [ -12 



Or closely in the ratio of 4 : 1 : \ : ■§-. This points to the formula,. 



4(Na 2 S0 4 ) + Na 2 C0 3 + i(NaCl) 

 as representing the composition of the crystals under examina- 

 tion. Neglecting the sodium chloride as non-essential, the 

 formula becomes : 



4Na 2 S0 4 + Na 2 C0 3 



which is probably the true one. 



The observed excess of soda is either due to errors of anal- 

 ysis, as only a small quantity was used, or it may have been 

 combined with boracic acid, as borax is very abundant at the 

 locality. 



The interesting anomaly of a sulphate and carbonate being 

 in chemical combination reminds us of the rare sulphato- car- 

 bonate of lead, leadhillite, to which this alone bears relation as 

 a natural species. 



The angles obtained were as follows: 



on 1= 90°. on 1=130° 30'. 



1 on 7=120°. on 2=113° 30'. 



Accordingly, the value of the vertical axis is 1*014:. Cleav- 

 age parallel to nearly perfect, but difficult to obtain. 



* All bases calculated as soda. Lime and magnesia were not present. 



