Photomicrographs of Unusual and Common Feldspars 

 PLATE I 



All photomicrographs taken with cross nicols, ocular X7.5, and objective, 

 16 mm, 



A. Zonal plagioclase liparite-perlite, Pushi Hrad, Hungary. (L-91) 



B. Zonal anorthoclase-crypto-microperthite in Kekequabec soda granite, 

 Minnesota. See Grant, Amer. GeoL, XI (1893), 383-89, and (at present unpub- 

 lished) Ph.D. thesis of Kennedy, University of Illinois (kindness of WiUiam S. 

 Bayley). Described as an "intergrowth of albite with either soda orthoclase 

 or soda microcHne . " (1150) 



C I. Adularia, St., Gottard Region, Eggerhorn, Switzerland. (Orgj.s 

 Abp.sAny.o.) Slide prepared with great care by the writer, showing phantom, 

 incipient microcline twinning. Considered as representing inversion of ortho- 

 clase (adularia) to microcline brought about by the grinding incident to prepara- 

 tion of the slide. (989) 



C 2. Same as G i. Slide prepared by W. H. Tomlinson, probably with less 

 care, showing greater development of phantom microcline twinning. (989^4) 



D I. Adularia, St. Gottard Region, Scopi, Switzerland. (Or 88 Ab 9 

 An 3.) Slide prepared by Tomlinson showing incipient twinning. (988) 



D 2. Same as D i, prepared with extreme care by the writer, showing not a 

 trace of phantom twinning. The parallel lines are cleavage cracks. (998 A) 



E. Crypto-microcline, pebble, Pacific Coast, phenocryst of a porphyry. 

 (A. F. Rogers.) (Approx. OrgoAbigAuz.) The light area in the center is 

 quartz. (1438) 



F. Moonstone (OrysAbjsAnz). Anorthoclase-cryptoperthite, from Ceylon. 

 See Kozu, Sci. Kept. Topoku Univ., Series III, Vol. I, No. i, showing incipient 

 development of perthite. (1394) 



G. Crypto-soda microcline, sanidine, Viterbo, Italy, showing development 

 of crypto-microcline twinning. 



^ O. Maschke, Pogg. Ann., CXLV (1872), 565-68; Weidematm's Ann., XI (1880), 

 722-34; J. L. C. Schroeder van der Kolk, Zeitschr.f. wiss. Mikroskopie, VIII (1892), 

 456-58. 



* Pyrometric (Seger) cone determination. Hence, as Makinen says, only approxi- 

 mate. 



3 Specimen 959. 



