iiai.u.k.. DUMORTIERITE. ( .> ( .> 
As we approach the middle of the dike the rock loses its schistose 
picture, becomes coarser, and we find occasional masses of dumor 
trite, which are more and more abundant, until finally we come to 
hat is called t h<- lower part of the dike, consisting of abundant dumor 
fcrite and quartz. Very rarely a small Mark tourmaline or garnet is 
ion. Muscovite is more or less abundant throughout the entire 
■per part, and in places forms an essential part of the rock. 
the lower part of the dike differs in many ways from the upper. 
o schistose structure is apparent; the rock is \<t\ coarse and has a 
ottled appearance, due to the dark bunches of dumortierite on the 
kite quartz background. 
Some masses of dumortierite are trery large, examples 5 by 3 by 3 
n. being not uncommon. They usually have m radiated columnar 
picture and break oil' nearly parallel to the base in fairly plane sur 
pes, which on large piece- become somewhat bowl shaped. A- the 
pious fibers are not strictl} parallel hut radiating, the breakage can 
ilv be approximately at right angles to the general elongation of the, 
Brs. These masses of dumortierite weather from the rock and 
and out very prominently. They usually have numerous cleavage 
sacks parallel to the base. The color of the mineral i- lavender, 
Bembling to some extent compact rubellite. Connected with this 
lusual color is the unusual pleochroism that the mineral possesses, 
iing from colorless to \-i-<\ purple instead of blue. 
Che quartz i- coarse grained and has a slight greasy appearance. It 
metimes occur- in large masses five from dumortierite. Magnetite 
present in small grains a- well a- titanium oxide rutile (?). An 
alysis of a -ample of pure quartz was made to prove the absence of 
y feldspar or other silicate. The analysis follow-: 
Si0 2 98. 78 
Fe 2 3 i total 15 
CaO 10 
MgO none 
Ti< ) 61 
I' l », trace 
99. 94 
Barer phase of the rock consists of quartz, muscovite, and dumor- 
rite. which is here present in -mall piece- hut n few millimeters or 
m thick. The mica i- here an essential constituent of the rock and 
iblaces becomes abundant. 
icroscopically the minerals present in the lower part of the dike 
I seen to be dumortierite and quartz, with muscovite and silliman- 
in small quantities, together with accessory magnetite, titanite, 
ile (?), apatite, and zircon, as well ;i- a number of -mull undeter 
• Med inclusions. The dumortierite occur- in irregular masses with 
: ged outline, often resembling in shape the hornblende of a diorite. 
