126 W. H. Hobbs—Mineralogical Notes. 
radial groups. They are many times the size of the musco- 
vite scales and are probably like the chloritoid metamorphic in 
their origin. A few acicular crystals of black tourmaline from 
a third of a centimeter to a centimeter in length occur in the 
mass of the rock and also as inclusions in the large chloritoid 
crystals. Jrregularly outlined masses of magnetite are likewise 
to be found both in the chloritoids and in the matrix of the rock, 
but those which are included in the chloritoids are surrounded by 
a zone of quartz, wnich was probably formed at the same time as 
the chloritoid as one of the products of the recrystallization of that 
portion of the rock now occupied by the large crystals of chlo- 
ritoid and its inclusions. Besides the large porphyritie chlo- 
ritoids, which are at times six centimeters or more across, a 
few small blades are disseminated like the biotite through the 
rock mass. 
The porphyritic crystals of chloritoid are tabular parallel to 
the base, of hexagonal outline, and are on an average about one- 
third as thick as they are long or broad. Their hardness is 
between five and six of Mohs’s scale. That they are generally 
twinned is seen in the examination of the hand specimen by 
the variation in the position of the plane of basal cleavage in 
different parts of the same crystal. In at least one specimen 
the twinning line is straight and runs parallel to one of the 
lateral faces (0 Px ). Before the mineral had been examined 
in section and the nature of its enclosures had been determined, 
a specimen was submitted to Mr. Louis Kahlenberg of the 
Chemical Laboratory of the University of Wisconsin for chemi- 
cal analysis. His results, which are given below, are therefore 
much affected by the included quartz and magnetite, which 
might have been excluded by treatment with the magnet and 
dissolving the residue as far as possible in sulphuric acid. The 
results are, however, sufficient to determine the mineral as 
chloritoid and are nearly identical with an analysis by Jackson 
of masonite from Natic, R. L, which like this was probably 
impure from admixed quartz and magnetite. 
SiO. (io ees et nee 35°52 
Al ‘O. 2 i) Soe Oe eee 29°53 
He, Oy 2. ost Rae eee Se 5°85) 
FeO. 2:2 gee aa eee 22°38 
MeO. 2.2: 22.2 aeeeeee 0°76 
CaO - 2. dees eee Gee eles 
EO... 2. eee 5°94 
BO 0. 8 20 eae trace 
