566 Washington — Constitution of Some Salic Silicates. 



shows clearly its relation to pseudo-leucite. Analcitc* has 

 exactly the same form of molecule, hut is a hyd rated sodium 

 leucite. On this interpretation hoth leucite and analcite are 

 to he regarded as molecular compounds rather than mixed 

 crystals or solid solutions, as is the case apparently with the 

 originally isometric, but unstable, pseudo-leucite. In this con- 

 nection attention may again be called to the isometric form of 

 the K 2 Al 2 Si.,0 8 molecule observed by Lemberg and mentioned 

 by "Weyberg.f 



The composition of maskelynite, a mineral only found in 

 meteorites, is somewhat uncertain. The formula as given 

 above agrees fairly well with the analysis, which was made on 

 a small amount of unsatisfatory material. 





Si0 2 



A1 2 3 



CaO 



Na,0 



K a O 



Found 



53-6 



25'7 



11-6 



5-1 



1-3 



Calc. 



55-6 



28-2 



10-4 



5-8 





The formula (NaSi) 2 (CaAl) (AlSi 2 8 ) 3 , which corresponds to 

 that of leucite above, leads to the composition : Si0 2 = 59*9, 

 A1 2 3 = 25-4, CaO = 7"0, Na 4 = 7'6. It is possible that this 

 is the true composition of the mineral, which needs reexamina- 

 tion, and that the figures found in the analysis, with lower 

 silica and soda and higher lime, are attributable to admixed 

 anorthite or labradorite. 



It must be noted that all the minerals of the leucite group, 

 in which the radical (R/ 2 A1) is prominent, are easily decom- 

 posed by acids, leucite without and analcite with gelatinization. 



It may be added that, from their study of the action of 

 ammonium chloride, Clarke and Steiger:}: conclude that : "anal- 

 cite and leucite are not true metasilicates, but pseudo-com- 

 pounds, either salts of a polymer of metasilicic acid, or 

 mixtures of ortho- and tri-silicates analogous to those which 

 we find among the plagioclase feldspars." Tschermak§ also 

 considers that leucite is not a true metasilicate, but a salt of 

 a polymeric acid, H 4 Si„0 6 , which he calls " leucitic acid." 



Nephelite Group, hexagonal. 



Nephelite, (artif.), (Na 2 Al) AlSi 2 B ( 2(KSi)AlSi 2 O e ) 



Kaliophilite, (K 2 Al)AlSi 2 O a , Nephelite (5:1) ■] 10(Na 2 Al)AlSi 2 O fi [ 

 Eucryptite, (Li 2 Al)AlSi 2 8 ( l(K 2 Al)AlSi 8 B ) 



Cancrinite, (Na 2 Al) 3 (CaAl) [(NaCO,)Al](AlSi s O s ) 5 .3H.O 



* The formula suggested here is in accord with the observation of Clarke 

 and Steiger (Bull. U. S. G. S., No. 207, 1902, p. 9), that one-half of the Na 

 of analcite is removed by heating in an open crucible with NH 4 C1. Unfortu- 

 nately no data are given as to the same experiment with leucite. 



•f Weyberg, loc. cit. supra. 



i Clarke and Steiger, Bull. U. S. Geol. Surv., No. 207, 1902, p. 19. 



gTschermak, Zeitschr. Phys. Chem., 1905, p. 364. 



