Í 
335 
blue opalescent quartz so characteristic a feature of the 
albite, which, while the subordinate CPA in the potassic- 
aplite, is the dominant felspar in the albitites. - 
The albite- “Pegmatites are to be rus from the 
potassic-aplites 
G.) By their prb minor developmeni—being limited 
or pipe-like 
ue ) By their coarse- Pris unge: potassic aplites 
being predominantly fine grained. 
(üi). =. bacs presence of accessory minerals as apatite, 
and rutile in relative abundance. Such 
uen te are practically absent from the 
microcline apli 
(iv.) By the absence of biotite. 
(v). By the absence of microcline. 
Varieties of Albitites.—The predominant type is a coarse- 
graiped quartz-albitite, which may pass into veins of pure 
albite. The quartz occurs in blue opalescent grains and the 
albite in ee twins—also twinned on the albite a 
e remaining t is a muscovite-albitite, in which mus- 
covite is associated with albite. The accessory minerals are 
developed in all types. 
eM echanism of Differentiation.—The residual magma, 
bers (24) within the granitic mass. Consequent on such fractional 
dietis the residual liquid was enriched in mineralizers, 
chie wate 
e main granite the crystallization of plagioclasé was 
early iulaled, and occurred with marked zoning, the varying 
composition being from andesine to oligoclase. The residual 
magma was thus enriched in albite molecules relatively to 
(29 In granitic masses the evidences of the existence w such 
Magma pools, as stipulated, are principally provided the 
occurrence of aplitie or pegmatitic phases with distinctly blended 
; rega to ite mass. ion, in 
situ, is therefore demanded. Where contacts between the aplitic 
or pegmatitic phase and the granite are sharp and well defined 
crystallization occurred after intrusion from such a magma p 
any nea masses show the evidences of two such types of 
satellitic phas 
