Thaumasite at West Patterson, JV. J. 231 



and s= 1*476. It must be stated, however, that a prism cut 

 from a crystalline aggregate cannot yield wholly satisfactory 

 results, as the light does not traverse a single individual, and 

 that for example which yielded the extraordinary value above 

 was vibrating in crystals whose vertical axes were approxi- 

 mately and not perfectly parallel to the edge of the prism. 

 Levy and Lacroix* give co = 1*507 and e= 1*468. 



In order to be absolutely sure of the uniform character of 

 the material for analysis, selected pieces of the mineral were 

 crushed and sifted to a uniform grain and separated by means 

 of methyl iodide CHJ, which was diluted with ether. That 

 every particle of the mineral in the separator floated at a 

 specific gravity of 1*887 and sank at 1*875, a difference of only 

 0*012, is sufficient proof of the homogeneous character and 

 great purity of the material. Lindstrom gives as the specific 

 gravity of the Swedish mineral 1*877 and Widman gives 

 1*83. 



The results of the analysis are as follows : 



I. II. III. Average. Ratio. 



Si0 2 ._ 9-23 9*33 9"23 9*26 *155 *97 



C0 2 6*87 6*77 6*82 *155 *97 



SO, 13*56 13-32 13*44 *168 1*05 



CaO 27*08 27*19 27*13 *484 3*04 



H 2 42*81 42*72 42*77 2*377 15*00 



Na 2 *39 *39 



KO *18 -18 



99*99 



The ratio of Si0 2 : C0 2 : S0 3 : CaO : H 2 is very nearly 

 1 : 1 : 1 : 3 : 15, demanded by the formula CaSi0 3 , CaC0 3 , 

 CaS0 4 , 15H 2 0. The analytical results are, moreover, very 

 close to those obtained upon the Swedish mineral by Lindstrom 

 and Hedstrom. A slight amount of alkali sulphate is prob- 

 ably present as impurity, therefore the alkalies have been 

 neglected in making the above calculation. That Na 2 and 

 K 2 are not isomorphous with CaO is shown by the following 

 experiment: 1*1765 gram of the powdered mineral were 

 treated in a platinum dish for over two days with cold water, 

 the insoluble mineral was then filtered off and the soluble por- 

 tion analyzed, with the following results : Si0 2 , 0*39 per cent ; 

 S0 3 , 0*56 ; CaO, 0*56; Na 2 O-f-K 4 0, 0*25. These indicate that 

 thaumasite is slightly soluble and that the alkalies have an 

 independent existence, for a quantity of Na 2 + K 2 equal to 

 about one-half of that found in the original analysis was 



* Les Mineraux des Roches, p. 286, 1888. 



