and the Results of its Alteration. 271 
found forming: parts of altered crystals, in which it has the 
avy laminated structure which is characteristic 
oO 
<j 
oO 
Qu 
ts) 
app 
erystals, evidently owing its origin in such cases to the alteration. 
An analysis of the fibrous variety of the species afforded Mr. 
Penfield the following results: 
G. == 2°687, . i Mean. Ratio 
SiO, 67°61 67°59 67°60 1°127 : 6° 
Al,O; 20°07 20°11 20°09 1195 1°03 
MgO 15 
Na,O 11°71 11°66 11°69 188 193 1°02 
2 3 | 1] hd. 
Ignition 14 14 14 
99°80 99 9°15 
This analysis i i eee fy ne formula Na,A1,Si,O,,, 
or that of albite 
he occurrence of albite pseudomorphs after spodumene is 
mentioned by Mr. Julien, but among the Massachusetts speci- 
mens they seem to play a comparatively unimportant part. 
Mr. Julien speaks of the albite as mixed with a little muscovite 
and quartz, and states hi these pseudomorphs are ‘‘a mere 
variety” of the coarse agglomerates of quarts, feldspar and 
mica, plea he calls pseudomorphs of vein granite 
At the Branchville locality the albite as an “independent 
siinehit Sabuptad a more common and perhaps more interesting 
place among the products of the alteration of the Sriginal 
spodumene 
The fibrous albite, of which the above analysis was made, 
formed the whole of a pair distinct crystal. A section 
A number of other ah of what we have called albite 
were also examined. The result proves that pure albite is 
rather rare, and that most of the granular albite in the crystals 
contains a considerable quantity of mica, and hence verges 
toward cymatolite. This qualification is to be remembered in 
seamining the plate. In many cases the albite is found to be 
n broad plates characteristically twinned, and with them are 
