﻿120 Cross and Eakins — Ptilolite, a new Mineral. 



sidering any definite portion of this water basic, although a 

 high temperature is necessary for its total expulsion. 



Heated before the blowpipe a tuft of the mineral shrinks 

 considerably and fuses to clear glass. Hydrochloric acid, even 

 boiling, has little or no action, but by strong sulphuric acid it 

 is gradually decomposed. Of course in a mineral of this de- 

 scription a determination of hardness is impossible and one of 

 specific gravity would be too inaccurate to be of any value. 



We propose as the name for this mineral, Ptilolite, derived 

 from nrikov, down, in reference to the light, downy nature of its 

 aggregates. 



Eeferring to the molecular ratio derived from the analysis, it 

 is seen that the empirical formula for this mineral is EO, A1 2 3 , 

 10SiO 2 + 5H 2 0, R representing Ca, K 2 and Na 2 . The sub- 

 stance belongs among the alumino-silicates of which no previ- 

 ously described hydrate contains so high a percentage of silica. 

 Perhaps the nearest allied hydrous mineral is stilbite, the com- 

 position of which may be expressed by the formula H 4 CaAl 2 

 Si 6 8 ,+4H 2 0. 



While the structural formulas for the complexer silicates are 

 as yet hypothetical, it is of interest to note the place assumed 

 by ptilolite in the scheme for the classification of the alumino- 

 silicates adopted by Tschermak* and others. By the combina- 

 tion of the Irydrous oxide H 2 A1 2 4 with two molecules of meta- 

 silicic acid, H 2 Si0 3 , through the elimination of 2H 2 0, there 

 results a simple alumino-silicic acid with the empirical formula 

 H 2 Al 2 Si 2 8 . By combining the same hydroxide with 4, 6, 8, 

 10, etc., molecules of H 2 Si0 3 there results a series of alumino- 

 silicic acids, the following anhydrous salts of which are known: 



Na 2 Al 2 Si 2 8 in socialite, 

 K 2 Al 2 Si 4 12 as leucite, 

 K 2 Al 2 Si 6 16 as orthoclase, 

 Li 2 Al 2 Si 8 O 20 as petalite. 



Other series are obtained by starting with other hydroxides 

 of alumina. 



Petalite stands alone in the above series as the representa- 

 tive of its type, and members with higher contents in silica are 

 yet unknown. Now the zeolites are in many cases simply hy- 

 drates of the above or closely allied salts, although the water 

 may be in part basic. No hydrate of petalite or of any corre- 

 sponding salt is known, but ptilolite is found to be the hydrate 

 of RAl 2 Si 10 O 24 which will be seen to be the next member in the 

 above series, following petalite. 



If such a classification of alumino-silicates be adopted, ptilo- 

 lite must be considered as the first member of a new group of 



* G-. Tschermak, Lehrbuch der Mineralogie, 2te Aufl., 244, 438, 490. 



