198 HAROLD L. ALLING 
The present-day conception of the chemical nature of the 
silicates is the result of slow development. In 1846 Laurent sug- 
gested that the silicates should be considered to be salts of several 
acids rather than a single one, and by 1865 ortho-, meta-, and 
trisilicic acid had become a firmly established nomenclature. 
Later Vernadsky? pointed out that in some aluminum-bearing 
silicates the element aluminum seemed to possess the characteristics 
ofanacid. ‘Thus the theory that some silicates are aluminosilicates 
instead of simple silicates was developed and is entertained by 
many geochemists. While it would be instructive to follow this 
phase of the subject in greater detail it is outside of the main pur- 
pose of this paper. However certain aspects of the alumino- 
silicate theory need to be considered in attacking the problem of 
the relationships between the soda, potash, and lime feldspars. 
‘““Schwantke? while reasoning over the réle of the lme-silicate 
which occurs mixed with the potash silicate K,AISi¢O,6 in orthoclase 
built up theoretical conclusions of much interest. ... . In order 
to make the formulas of albite, anorthite, and orthoclase more 
analogous to each other, we may write them Na,AL,SiSi,O., 
K,ALSi,Si,O,6, Ca,ALALSi,O.%, and Ba,ALALSi,O;6.’”4 
Bayley® says that chemically, the feldspars may be regarded 
as isomorphous mixtures of the four compounds, KSiAISi,0s, 
NaSiAlSi,Os, CaAlAISi,Os, and BaAlAISi,Og, each of which except 
the fourth has been found nearly pure in nature..... The feldspars 
have also been regarded as salts‘of the acid H;AISi,O3 in which the | 
hydrogen is replaced by various radicals, thus (KSi)AISi,0s, 
orthoclase; (NaSi)AISi,Os, albite: (CaAl)AISi,Os, anorthite; and 
(BaAl)AISi,Os, celsian. There are several objections to Bayley’s 
conceptions. In the first place, as will be pointed out later, the 
t Laurent, “Sur les Silicates,” Comp. Rend., XXIII (1846), 1050-58. 
2 W. Vernadsky, “Uber die Sillimanitgruppe und die Rolle des Aluminums in den 
Silicaten,”’ Bull. d. Russ. Ges. d. Naturf., 1891, nr. 1-100. (In Russian.) 
3 A. Schwantke, ““Die Beimischung von Ca in Kalifeldspath und die Myrmekit- 
bildung,” Centralbl. fiir min. Geol. und Pal. (1909), pp. 311-18. 
4J. J. Serderholm, ‘‘On Synantectic Minerals,” Bull. de la commo. geol. de Fin- 
lande No. 48, 1916, pp. 90-91. 
5 William S. Bayley, Descriptive Mineralogy, Appleton (1917), p. 408. 
ita iae ee e 
