[graham] a new ZEOLITIC MINERAL 189 



Molecular ratio. 



SiOo 



AI2O3 



CaO 



MgO 



NaoO 



K2O 



H2O 



100-87 



The water was fractionated as follows, heating at each temper- 

 ature being continued for two hours: — 



The mineral commences to lose water at, or below, 100°, and 

 continues to do so at a fairly uniform rate until a temperature of 

 205° is reached, when 6-5 per cent., or almost exactly one-half, of the 

 water has been driven off. At 275° the additional loss has been less 

 than 1 per cent., and the 5-71 per cent, of water still retained by the 

 mineral corresponds to 0-317 molecules, or 2-83 molecules on the 

 basis AI2O3 = 1-00. 



Ferrierite thus has all the general characters of a zeolite; but it 

 differs from all known zeolites in containing MgO in place of CaO, 

 which is entirely absent from the mineral. In composition it is very 

 closely related to mordenite and ptilolite, both of which have been 

 shown by Clarke^ to be simply representable by the general 

 formula Al2(Si205)5R'4+«Aq., where R'2 = Ca, Na2, K2, H2 and n 

 = 6 or 3. 



In ferrierite, the molecular ratio AI2O3 : Si02 = l : 10, as required 

 by this formula; the molecular ratio AI0O3 : MgO is approximately 

 1 : f , and the ratio AI2O3 : (Na, K)20 approaches the same value. 

 For exact correspondence with Clarke's formula, it would be necess- 

 ary to assume that 1 - 35 per cent, of the water contained in the mineral 

 is basic. Ferrierite might then be given the formula Al2(Si205)5R'4- 

 + 6H2O, where R'2 = Mg : Na^ : H2=l : 1 : 1 ; the theoretical per- 

 centage composition calculated for this formula is as follows: — 



M;«. Jour. Sci., 3rd Series, vol. 44, 1892, p. 101. 



Sec. IV. Sig. 14 



