100 CONTRIBUTIONS TO MINERALOGY. [bul 
Again, it forms fun-shaped radiating masses, sometimes of large i 
Irregular broken fibrous masses also occur scattered through the s 
The quartz is allotriomorphic and is but slightly cracked. It is ra 
full of inclusions in places. With the exception of a little muscc 
there are no secondary minerals present. 
The common form for the dumortierite is shown in radiated far 
masses that vary considerably in size. When the entire piece is la 
than a quadrant, parts of the black cross (seen in spherulites) are 
when the nicols are crossed. These fan-shaped pieces are prob 
the results of an incomplete spherulitic growth. The most perfect 
consists of but half a circle. On certain parts no radiated fibers 
detectable, the (prismatic) cleavage lines being perfectly para 
Some of the pieces become decidedly fibrous toward the ends, and 
various individual libers depart somewhat from true parallelism, 
between these fibers fine-grained aggregates of muscovite can o 
be seen. 
A number of pieces showed a (secondary I) growth of libers, w 
are probably in all cases dumortierite, as with high poweis a i 
pleochroism can be detected. They were at first thought to be i 
manite, but they agree in all their properties — so far as can be d( 
mined — with dumortierite. These fibers can be classed in two pi 
Those in the first part seem to have been formed as a sccon< 
growth on the main masses of dumortierite. The fibers branch 
considerably and often form a radiating fringe around an entire 
tion of the mineral. They penetrate the quartz grains, and inters! 
muscovite is absent. The line where they join the main mass of 
mineral is usually fairly well defined. In general, the fibers are 
mal to the edge of the main mass, but locally they vary considera 
especially where they form fanlike groups. 
The fibers of the second class clearly represent a stage in the alt 
tion of the dumortierite to muscovite. The solid mass of dumortl 
becomes fibrous and, at the edges, breaks up into small fibers, w 
gradually become loose from the parent mass. The space where 1 
formerly joined is now occupied by a granular mass of musco^ 
which also fills the spaces between the fibers. Gradually this pro 
goes on until, finally, we have a large mass of granular muscovj 
which are embedded a few fibrous prisms of the original mint 
Fig. 6 shows diagrammaticall y a stage in the process. 
Basal sections present an entirely different appearance. The ma 
pinacoidal cleavage, so well developed on the New York mineral, 
not show on the sections of the California mineral. The impel 
prismatic cleavage is present and divides the section up into a m 
tude of irregular bodies. Occasionally there is a short crack pai 
to the brachypinacoid, and it may be that the mineral possess* 
imperfect interrupted brachypinacoidal cleavage. 
