304 HAROLD L. ALLING 



in detail at present, it is obvious that further researches would bring 



us very interesting and important results "^ It is evidently 



a metastable solid solution under molecular stress, tending to 

 develop into a two-phase system, but prevented from doing so by 

 the high viscosity which is characteristic of the solid state. 



The investigation of these moonstones calls our attention to the 

 feldspars called cryptoperthites. Such feldspars represent transi- 

 tional stages from the unstable solid solution, anorthoclase, to stable 

 perthite and which without much doubt can be classified as solid 

 coUoids — ^almost isocolloids. The passage from anorthoclase to 

 perthite is through the intermediate stages of crypto-and micro- 

 perthite; from a "molecular" dispersed system through a colloidal 

 dispersed state to a mechanical intergrowth. 



While X-ray analysis throws much-needed Ught upon internal 

 arrangement of the atoms the question of the degree of equilibrium 

 attained by each given specimen is still unsolved, for these minerals 

 have different origins and, as already pointed out, furnish data for 

 different diagrams. Here is a problem for the future, in the solution 

 of which the Tohoku University investigators should have a promi- 

 nent share. 



In addition to their X-ray analyses these Japanese workers have 

 conducted a series of thermal experiments that agree in large meas- 

 ure with the results obtained by Vogt, Dittler, Johannsson, Vegard, 

 Watts, Douglas, Makinen, and the writer.^ 



' S. Kozu and K. Seto, "Sanidine from the Eifel," Science Repts., Tohoku Univ. 

 (Sendai, Japan), Ser. Ill, Vol. I, No. i, p. 27, 



= J.H.L.Vogt,"Physikalish-chemisclie Gesetze der Krystallisationsfolge in Eruptiv- 

 gesteinen," Tsch. Min. Petro. Mitt., XXIV (1905), XXV (1906), and XXVII (1908); 

 E. Dittler, "Die Schmelzpunktskurve von Kalinatronfeldspaten," ihid., XXXI (1912) ^ 

 513; "Uber die Darstellung kalihaltiger basischer Plagioklase," Min. und Petro. Neue 

 Folge., XXIX (1910), 273-333; "tJber das Verhalten des Orthoklase zu Andesin und 

 Celsian iiber seine Stabilitat in kiinstlichen Schmelzen," Tsch. Min. Petro. Mitt., XXX 

 (1911), 118-27; H. E. Johansson, "Om faltspaternas sammansattning och bUdings 

 forhaUanden," Diese Zeitschr., XXVII (1905), 338; Vegard, "Die Konstitution der 

 MischkrystaUe," Phys. Zeitschr., XVIII (No. 15, 1917), 93-96; A. C. Watts, "The 

 Feldspars of the New England and North Appalachian States," U.S. Bur. Mines Bull. 

 g2, 1916; J. A. Douglas, "On Changes of Physical Constants in Minerals [by heating]," 

 Quar. Jour. Geol. Sac, LXIII (1907), 159; Eero Makinen, "Uber die Alkalifeldspate/' 

 Geol. For en. Forhandl., XXXIX (191 7), H. 2. For synthesis see F. W. Clarke, "Data 

 of Geochemistry," U.S. Geol. Surv. Bull. 606, 364-67. 



