J. P. Cooke, Jr., on Cryophyllite, 227 
proving that the water must be chemically, and not merely hy- 
groscopically, combined ; secondly, because while water of crys- 
tallization would be present in a definite number of equivalents 
——one or more—the quantity of water in this mineral obeys no 
such law, and only amounts to a small fraction of a single equiv- 
alent; lastly, because the water is only driven out at a high tem- 
erature, indicating that it is in a state of intimate combination. 
here does not appear to be any simple relation between the 
amounts of the protoxyd and sesquioxyd of bases in the Rock- 
port lepidomelane; but the general formula of the mineral may 
readily be reduced to that of the magnesian micas by assuming 
that a portion of the protoxyd of iron has been replaced by the 
have called cryophyllite, and this being the case we may expect _ 
berg* and others in regard to the crystallization of isomorphous 
salts when mixed sSuathee in the same solution. It appears from 
these investigations that isomorphous salts do not necessarily 
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experiments furnish an exact counterpart of the conditions 
which we actually realize in the Rockport granite. 
Albite—The general nature of the vein in which the best erys- 
tals, both of eryophyllite and lepidomelane, have been found, 
has already been described in the earlier part of this paper. 
This vein ‘consists chiefly of quartz and fel of the ortho- 
* Pogg. Ann., vol. xci, p. 321. 
