Properties of the Feldspars. 119 



phate fusion nor the digestion with acid and ammonia appeared 

 to have changed the particles in the slightest degree. Diligent 

 search was made for opaque or amorphous matter on the sur- 

 face of the grains, or any other indication of decomposition, 

 but none was found. While the chemical analysis indicates a 

 rather higher purity for the first product, purified by fusion, 

 the differences are nearly within the limits of error and there- 

 fore hardly conclusive. Both powders were ground finer than 

 usual for the specific gravity determinations to avoid errors 

 introduced by a spongy structure. 



Reverting now to Hautefeuille's directions, it is clear that 

 glass of albite composition crystallizes homogeneously under 

 substantially the conditions which he obtained, as well or better 

 than the mechanically mixed component parts ; but the part 

 played by the tungstate requires some further experimental 

 study before a conclusion can be reached. 



Except for the specific gravity, the experiments upon crys- 

 talline albite and orthoclase which follow were made upon 

 natural specimens from well-known localities (a fragment of 

 the Mitchell Co. albite is shown in Plate I, 1), for which we 

 are indebted to Dr. G. P. Merrill of the National Museum 

 and Dr. Joseph Hyde Pratt, State Mineralogist of North 

 Carolina. The specimens were selected with great care, but 

 like all natural specimens, they contained other feldspars and 

 inclusions. The analyses follow : 





Alhite. 

 (Amelia Co., 

 Va.-Nac. Mus.) Calculated, 

 Found. Anhydrous. 



Albite. 

 (Mitchell Co., 

 N. C.-Pratt.) Calculated, 

 Found. Anhydrous. 



Microcline. 

 (Mitchell Co., 

 N.C.-Nat.Mus.) Calculated, 

 Found. Anhydrous. 



Si0 2 . 





68-22 



68-71 



66-03 



66-42 



65-49 



65-83 



A1 S 8 . 





19-06 



19*20 



20-91 



21-03 



17-98 



18-07 



Fe 2 3 





•15 



•15 



•18 



•18 



•30 



•36 



CaO ._ 





•40 



•40 



200 



2-00 



•42 



•42 



Na 2 0. 





11-47 



11-53 



9-97 



10-03 



2-29 



2-30 



K 2 0._ 





•20 



•20 



•70 



•70 



12-95 



13-02 



H 2 0-_ 





•69 







•59 







•51 







100-19 100-38 100-00 



It will be remembered that in the preliminary experiments 

 (p. 98) the heating curve of these natural feldspars did not 

 show an absorption of heat which we were able to detect ; our 

 first step was therefore to find out what manner of process it 

 was by which a charge of crystalline albite or orthoclase 

 became amorphous without leaving a thermal record behind. 



We prepared a charge of albite glass from a previous melt 

 powdered to "100-mesh." In this glass powder a small crystal 

 fragment (perhaps 2 x 5 x 10 mm ), from the same original speci- 



