SPHERULITIC CRYSTALLIZATION. 461 
those in larger crystalline spherulites, their arms shortening 
and lengthening out according to the distance of the bound¬ 
ary from the center of crystallization, which may be quite 
excentric. 
We should therefore consider the essential characteristic 
of spherulitic growths to consist in the formation of radiating 
or diverging groups of crystals, which commenced to crystallize 
from one or more points. Thus it may be from a single 
center or from a number of different ones more or less distant 
from one another. The component crystals are usually pris¬ 
matic and form delicate rays or fibers, with which may be 
associated other forms of minerals with or without definite 
orientation; but an arrangement of plate-like crystals or 
grains that are oriented with reference to a center of crys¬ 
tallization may also constitute a spherulitic growth. 
A diverging fibrous crystallization which has started from 
innumerable points close together over a plane would pro¬ 
duce a growth of fibers which would lie approximately par¬ 
allel to one another. Such structures appear in thin section 
like bands or fringes of almost parallel fibers, and constitute 
a special form of spherulitic. crystallization. 
Summary. 
The chief facts brought out by this study may be stated as 
follows: 
The occurrence of tourmaline as a primary constituent of 
the rock in small amounts and sporadically, with the similar 
occurrence of mica. 
The compact granophyric spherulites are composed of 
prisms of orthoclase elongated in the direction of the clino- 
axis, which radiate from a center of crystallization. With 
the feldspar is quartz, intergrown as in granophyre or micro¬ 
pegmatite. 
The branching growths of feldspar needles which form the 
rays of the porous spherulites, and which also occur alone, 
are formed of prisms of orthoclase, sometimes elongated par- 
59 — Bull. Phil. Soc., Wash., Vol. 11. 
