cuau*.] MISCELLANEOUS SPECIES. 67 
diorthosilicates; the vanadium in ardennite maybe combined as V0 3 or 
as V0 4 , or it may form part of a complex vanadio-silicic acid, and between 
these alternatives there is no present means of deciding. To carpholite 
the formula H 4 MnAl 2 Si 2 O 10 is commonly assigned, but the analyses vary 
from this composition too widely. Even with this formula carpholite 
may be either an orthosilicate or a basic metasilicate, and we can only 
say with regard to this species that further investigation is necessary. 
Spodumene, acmite, jadeite, and the corresponding members of the 
amphibole group will be considered in connection with the metasilicates. 
It is quite possible that these minerals are really pseudo metasili- 
cates, and that they should properly be discussed now. Their study is 
deferred on mineralogical grounds solely. 
Three other salts of triad bases may be noted here, as having more 
analogy with the salts of aluminum than with any other silicates. They 
are pseudobrookite, an orthotitanate of iron, Fe 4 (Ti0 4 ) 3 , and the bismuth 
silicates, eulytite and agricolite, Bi 4 (Si0 4 ) 3 . The two last-named species 
differ in form but are identical in empirical composition. They, there- 
fore, suggest two types of chemical structure among the silicates of 
trivalent bases. 
