and the Results of its Alteration. 279 
comparatively unstable compound, since it changes so readily 
to muscovi 
The second on in the alteration was the formation of cymat- 
olite out of dumene; this change consisting in the substi- 
tution of potelo! at (and hydrogen) for the remaining equiv- 
alent of lithium in eucryptite, and the consequent formation of 
muscovite. The result is a compound, in equal molecular 
that this compound substance, as derived from different local. 
ities, should be of so uniform chemical character. The 
explanation for this is to be found in the nature of the chemical 
process by which the alteration was brought about, the reaction 
going on uniformly through the mass, without, in ‘the m ajorit 
of cases, any distinct segregation of the two constituents formed. 
The change to o B spodumene must have been produced by the 
action of a soda solution, and the subsequent change to cyma- 
tolite by that of a solution containing potash. 
We have now to speak of the pseudomorphs in which the 
resulting minerals, mica and feldspar, appear in distinct form, 
and not as almost irresolvable aggregates. It was first remarked 
in regard to the cymatolite that in its usual varieties the mixture 
between the muscovite and albite was an extremely close and 
uniform one. This is ordinarily the case — respect to the 
normal material, as is exhibited in hundreds of specimens. 
There are others, however, of which this is feng true, but where 
the silvery luster due to the mica is more or less absent, and the 
substance approximates in character to eae albite; and, on 
the contrary, there are others where the albite is nearly absent 
and the mica is nearly pure (see fig. 20). The conclusion to 
which these facts have led us is that there are many gradual 
the conditions should be such as to lead occasionally to such 
segregations was to have been expected. It is rather remark- 
able that they are comparatively rare, and that normal cymat- 
olite is the rule. 
scheme, presented above, obviously ie gps that the 
muscovite and ‘albite should be formed in equal parts molecu- 
mica not infrequently observed in igen with large masses 
of albite. It appears, to be sure, in separate form as a scaly 
covering of fracture-surfaces through the sdseted crystals, and 
occasionally in small segregated masses, but the amount so 
observed is much smaller than the equation si ap 
