354 HAROLD L. ALLING 



It is a little difficult to understand why the majority of Amer- 

 ican mineralogists seem to favor the view that the two silicate 

 radicals (SiaOg) and (SiOJ are mutually equivalent. It was an over- 

 sight, however, for Wherry to include the writer in this group. 



The writer believes that Wherry has reached a very reasonable 

 explanation of the isomorphism of the series. 



THE POTASH-LIME SERIES 



This system, called the "oranite" series in Part I, is the one 

 that is rarely recognized. Several illustrations, however, from the 

 Adirondacks were there recorded. Such feldspars are intergrowths 

 and mechanical aggregates, not homogeneous single-phase solid 

 solutions.^ 



Wherry^ in the July and October numbers of the American Min- 

 eralogist took exception to some of the statements in Part I. These 

 criticisms, based upon misunderstandings, have been reconsidered 

 and corrections have been made in the December number.^ We are 

 essentially in agreement. 



Granite is not a hypothetical intergrowth. A dozen slides in the 

 writer's collection contain examples. Furthermore various investi- 

 gators, including Dittler"* and the writer, have succeeded in synthe- 

 sizing them in the laboratory. They correspond to perthite. 



The reason for giving this system a name is as follows: The 

 Adirondack occurrences consist of labradorite (MisAb4sAnso) with 

 blebs of potash feldspar (OrgsAbgAnio) imbedded in it. This inter- 

 growth is approaching, as a limit, the potash-lime binary system; 

 hence a name is very desirable and quite analogous to perthite. 



The results of thermal studies on artificial feldspars by the investi- 

 gators above mentioned show that on adding orthoclase to bytownite 

 or to anorthite zonal grown crystals can be made up to 10-15 per 



' See page 236 of Part I. See Harker, op. cit., p. 246; William S. Bayley, Descrip- 

 tive Mineralogy, 191 7, p. 408. 



2 E. T. Wherry, Amer. Min., Vol. VII, No. 7 (July, 1922), p. 115. .\lso Wherry 

 misquotes the writer in Rev. GeoL, January, 1923, p. 30, No. 22. 



3 E. T. Wherry, Amer. Min., Vol. VII, No. 12 (December, 1922), p. 212. 

 "Emil Dittler, "tJber die Darstellung kalihaltiger basischer Plagioklase," Mmj. 



und Petro., Neue Folge., XXIX (1910), 273-333; "Uber das Verhalten des Orthoklase 

 zu Andesin und Celsian uber seine Stabilitat in kiinstlichen Sclimelzen," Min. Petr. 

 Mitt., XXX (1911), 118-27. 



