3CHU.LER] DUMORTIERITE. 103 
The rock in which they occur is a light-colored^ fine-grained rock, 
containing, besides the blue spherulites, patches of a compact, soft, 
light-green mineral, shown to be muscovite. While the exposed sur- 
face of the rock is dark, the fresh portion light gray, rarely becoming 
llmost white. Sometimes the dumortierite occurs so abundantly as to 
bolor the entire rock blue. Pja-ite is also present and in places is very 
ibundant. 
ruder the microscope the rock is seen to be very tine grained and 
to consist of quartz, muscovite, and andalusite in nearly equal propor- 
tions. The porphyritic spherulites of dumortierite form a striking 
feature in the fine-grained rock. The pale-green patches before men- 
tioned are seen to be muscovite. Pyrite is abundant, and a few grains 
bf magnetite (ilmenite?) surrounded by leucoxene are also present, 
[n places the leucoxene is abundant. 
The andalusite occurs as short laths with a square cross section and 
ilso as irregular more or less opaque masses without definite shape, 
rhey are probably in some stage of alteration, possibly to muscovite. 
While usually very minute, the laths occasionally become quite large 
relatively. In general, the andalusite surrounding the larger spheru- 
ites is much coarser than the main mass, though there are numerous 
exceptions. When clear and transparent, the laths exhibit the normal 
properties of andalusite. The relief is moderate and the birefringence 
ow. Imperfect prismatic cleavage is sometimes seen. The prisms 
ire nonpleochroic and pleochroic halos are absent. Extinction is 
ilways parallel. The elongation is always in the direction of maximum 
elasticity. 
Sillimanite seems to be entirely absent. Muscovite occurs in the 
yreen masses and also in minute particles distributed throughout the 
entire rock. Nowhere does it occur in plates, as it normally does in 
granite, but everywhere it is in minute pieces. A good deal is prob- 
ably derived from the alterations of the andalusite and dumortierite, 
md it may be possible that all of it is secondary — that the rock origi- 
nal ly consisted essentially of quartz and andalusite. An anah T sis of 
:he green mineral was made on a small amount of material, containing 
ilso some andalusite and quartz. It shows the mineral is muscovite. 
:hus corroborating the microscopic evidence. 
Si0 2 50. 13 
A1 2 3 32. 37 
Fe 2 3 (total ) 1 . 52 
MgO 09 
CaO 15 
H 2 0- 1. 74 
H 2 0+ 5. 08 
K 2 9. 60 
100. 68 
Specific gravity 2. 80 
