68 A. S. Ecikle — Erionite, a new Zeolite. 



while Ca + Mg:K 2 :Na 2 = 2: 1 : 1. This gives a general for- 

 mula 6Si0 2 , Al 3 3 (CaK a Na )0 + 6H a O, or allowing one molecule 

 of water as hydroxyl, H 2 Si 6 Al 2 CaK 2 Na 2 J1 + 5li 2 0. Tlie gen- 

 eral formula is analogous to that of stilbite, in which the 

 calcium has been largely replaced by the alkalies, but in other 

 respects the zeolite has no resemblance to stilbite and is 

 undoubtedly a distinct mineral. The specific gravity is 1'997, 

 determined by the methylene iodide and Thoulet solutions. 

 Unfortunately the filaments are so delicate that complete opti- 

 cal determinations cannot be made. The mineral has a mod- 

 erately strong double refraction. The acute bisectrix lies 

 parallel to the fibers, since an axial figure normal to the obtuse 

 bisectrix can be seen in the fibers. The axis of least elasticity 

 is apparently in the direction of the fibers, making the mineral 

 positive in character. Extinction is exactly parallel and indi- 

 cates an orthorhombic crystallization. Several attempts were 

 made to get a cross section of a bunch of the fibers, by imbed- 

 ding them in various media, but nothing in the way of an 

 axial figure was obtained. No difference was observed in the 

 polarization colors between the fibers heated to 280° C. and 

 those not heated. 



The name erionite, from epiov, wool, is proposed for the 

 zeolite, on account of its woolly appearance. 



An analysis of the milky opal associated with the mineral 

 gave Si0 2 95*56, H 2 4*14 per cent and a trace of alumina. 



Mineralogical Laboratory, Harvard University, April, 1898. 



