240 HAROLD L. ALLING 
On the other hand the conception of a definite chemical com- 
pound within the series has been expressed by a number of min- 
eralogists. Miers™ says 
hyalophane corresponds to the formula K,BaAl,SisO., (not isomorphous 
[K.,Ba]) and this can be expressed as a mixture of BaAI,Si,O3 with 2 (KAISi,Os), 
i.e., as compounded. of two molecules of orthoclase with one molecule of barium 
silicate similar to anorthite. This union is exactly analogous to the mixture 
of albite and anorthite in the (plagioclase) group . . . . but in hyalophane 
the mixture appears to be only in one definite proportion, so that the mineral 
is to be regarded as a double salt tather than a solid solution. 
A similar view is taken by Moses and Parsons? who give hyalo- 
phane the following formula: (K.,Ba)AL(SiO,), as though the 
fundamental acid was metasilicic. Let us see how such an inter- 
pretation is possible. If we employ one unit of the barium and 
two of the potash components then 
2X (KAISi,Os) = K.AI,SicOy6, a trisilicate 
Pa etcn , an orthosilicate. 
Now ; | 
Aiba Nl ekOu_KBaAl,(SiO)s 
And furthermore 
see = (K,Ba)Al,(SiO,),, 
which looks like a metasilicate but it may be far from being one. 
By taking two trisilicate units and one orthosilicate unit we get the 
result. The writer must take exception to such an interpretation. 
Furthermore Moses and Parsons indicate by the comma between 
the K, and Ba that the ratio between them is not constant. In 
other words the ratio of the number of units of the two components 
varies. If it varies then the so-called formula would be much 
more complex and depart from the form assumed by a metasilicate. 
tH. A. Miers, Mineralogy, p. 461. 
2A. J. Moses and C. L. Parsons, Mineralogy, Ceysialieenae and Blowpipe 
Analysis, fifth ed., p. 493, 1916. 
mid we 
