Morey £ Bowen — Melting Potash Feldspar. 5 



contains about 10 per cent albite. The composition of 

 these minerals is shown in Table I. The last two analy- 

 ses were made by Dr. H. E. Merwin in connection with an 

 investigation he has not yet published. The results of 

 his analyses, together with some of the material, he has 

 kindly turned over to us. 



Table I. — Analyses of natural feldspars, 



I II 



Microcline Sanidine 



(Mitchell Comity, (Laacher See, 



North Carolina, U. S. A.) Ehineland) 



SiO, . . . 65.83 64.21 



ALO, 18.07 19.10 



Fe~0 36 



Cab". 42 .24 



Xa,0 2.30 1.76 



K,6 13.02 14.60 



III 



Adularia 



(St. Gotthard, 



Switzerland) 



64.24 

 19.21 



none 



1.45 



14.90 



100.00 



99.91 



99.80 



I. E. T. Allen analyst. Recalculated to anhydrous basis. 

 Day and Allen, op. cit. p. 48. The microscope shows that a very 

 little of the albite is present as perthitic stripes. 



II and III. H. E. Merwin analyst. 



The details of the experiments on these three natural 

 feldspars and our artificial material are given in Table II. 

 It may be noted here that all four show the breaking up 

 of the feldspar into liquid and leucite. The temperature 

 at which this occurs is not greatly different in the differ- 

 ent feldspars, being lowered only a little by the presence 

 of albite. The evidence points to about 1170° as the 

 proper temperature for pure potash feldspar. There is 

 moreover no appreciable difference of behavior connected 

 with the difference in form of orthoclase and microcline. 



All of the feldspars show a very large temperature 

 interval in which the mass consists of leucite and 

 liquid. A full discussion of the change of habit of the 

 leucite with increase of temperature has already been 

 given for the pure artificial material. Natural crystals 

 usually give more perfect leucite forms than the pure 

 material when exposed to a given temperature for an 



