THE MINERALOGRAPHY OF THE FELDSPARS 303 



KAlSijOs end higher than the soda rich ranges. This can be ex- 

 pressed in other words: the temperature range of inversion is 

 lowered by an increase of soda. This is contrary to Makinen's dia- 

 gram. It is not the purpose here to emphasize this point unduly, 

 but merely to suggest where additional light is desired. 



Let us briefly examine the diagram of Marc.^ Here the dimorph- 

 ism of both components of the system is indicated. He says (in 

 translation), "Whether the transition point i (Fig. i in Part II) is 

 situated above the melting point h has not been determined." The 

 temperature scale as originally given is only approximate and con- 

 sequently the writer has taken the liberty of shifting it to more 

 nearly match that of Makinen. 



X-RAY ANALYSIS 



Kozu, Endo, Suzuki, and Seto^ have investigated specimens of 

 adularia, moonstone, and sanidine with the X-ray spectroscope. 

 Their discoveries are important. The adularia (Orgg-s Ab^.j An2.4) 

 from St. Gottard was shown to have a single space-lattice which was 

 unaltered by heating over the whole temperature range of its crystal- 

 line state. A Ceylon moonstone (Or74.4 Ab23.i Auz.g), however, 

 exhibited two space lattices^ at all temperatures below 700° C. 

 Above this temperature it became a single space-lattice system. A 

 thin section of a moonstone from Ceylon"* which may have been 

 similar or identical with the material studied by Kozu et al., proved 

 to be a cryp toper thite, microscopically agreeing well with the results 

 of X-ray analysis. A moonstone from Korea (Orei.g Abjz.y Ans.4), 

 a feldspar still richer in soda, exhibited the same property but the 

 temperature of the passage from a two-space lattice structure to a 

 single-space lattice system was about 500° C. In contrast to the 

 latter, a sanidine from the Eifel (Or^e.g Abai.g Ani.3) behaved as 

 though it was a homogeneous solid solution of orthoclase and "bar- 

 bierite. " " As is well known, however, the Eifel sanidine has a pecul- 

 iar optic property, easily variable optic axial angle with the change 

 in temperature, that is, an unstable molecular structure with respect 

 to temperature. Though we cannot enter into the discussion of this 



'Robert Marc, Chemische Gleichgewichtslehre, 1911, p. 102. 



^ Science Reports of Tohoku University (Sendai, Japan), Series III, Vol. I, No. i. 



3 As shown by two sets of Laue photographs. A cryptoperthite. 



■i Purchased from Ward's Natural Science Establishment. Specimen No. 1394- 



