368 



HAROLD L. ALLING 



that potash feldspar melts can absorb or have a selective ability to 

 dissolve iron-bearing minerals. Such a theory would explain the 

 colorization of orthoclase and microcline in granites, syenites, etc. 

 In contrast to this idea is the light that is cast when the ferric feld- 

 spars are considered. As long as feldspars are considered as salts of 



TABLE V 



Orthoclase, Madagascar 



36 



SiO.. . 

 ALO3. 



FeA- 



FeO.. 



MgO. 



CaO.. 



BaO. 



Na.O. 



K^O.. 



H.O.. 



Total. 



KFeSijOs.. 

 KAlSijOg.. 

 NaAlSijOg. 

 CaAUSUOg. 

 BaAUSbOg. 



Total. . 



Excess SiOa . 

 Excess AI2O, 



64.19 



16.62 



2.88 



0.18 



63-99 



18.02 



0.97 



0.00 



n.d. 



0.34 

 15.81 



0.50 

 0.06 

 1.86 

 14-32 

 0.51 



64.76 

 17.98 

 1. 18 

 0.09 

 0.08 

 o. 16 

 n.d. 

 1.07 



15-39 

 . 20 



100.23 



100.91 



11.02 



82.50 



S-05 



81.37 



10.74 



2.48 



0.15 



4-54 



86.63 



9.06 



0.79 



96.41 

 1.92 

 1.32 



100.76 



99-65 



64.72 

 17.97 

 I. 20 

 0.09 

 0.09 

 o. 10 

 n.d. 

 0.94 

 iS-i8 

 o. 19 



100. 



4.61 



55-45 

 7.96 



-49 



i-5i 



1. Lacroix, Min. de la France, XXIX (1913). Boiteau, analyst. Deep lemon 

 yeUow. (Kindness of Henry S. Washington.) 



2. Lacroix, Min. de Madagascar, I (1922), 560. Raoult, analyst. Nearly color- 

 less. (Kindness of Henry S. Washington.) 



3. Material from Ward's Natural Science Establishment. Madagascar Mining 

 Co. Analysis by H. B. Croasdale, Eraser Laboratories, New York City. 



ortho- and trisiKcic acids the non-replaceabihty of the aluminum by 

 ferric iron is indeed striking. The apparent absence of such feldspars 

 is more understandable if these minerals are alumino-silicates. How- 

 ever, KFeSi308 has been synthesized by Hautefeuille and Perrey' 



' P. Hautefeuille and A. Perrey, Compt. Rendu. (1888), 107, 1150, and Zeitschr.f. 

 Kryst. XVm (1891), 329. 



