98 
Rex T. Prider. 
The following types are developed amongst the mica schists : — 
(a) Sillimrmite Schists . — These are mainly two-mica schists with narrow 
psammitic bands. Slight variations have been noted and they are illustrated 
by the following descriptions of typical members : 
(i) Quartz-biotite-sillimanite schists (e.g., spec. No. 15638). The‘s<^ 
are finely schistose structured rocks consisting of bands composed 
almost entirely of fine acicular sillimanite, alternating with quartz- 
biotite bands which represent more ferruginous and psammitic 
layers in the original sediment. The fibrolite bands are occasion- 
ally distorted by a later growth of sillimanite in stout cross fractured 
prisms arranged at about 45° to the schistosity (figure 7A), in- 
dicating that a later thermal metamorphism was imposed on the 
earlier regional metamorphism which had developed the fibrolite. 
Muscovite (rare) also has a tendency to be arrang(‘d with its 
cleavages at about 45° to the schistosity. 
Fig. 7. 
A. Sillimanite schist — bands of fibrolite with a little biotite, 
alternating with quartz-biotite bands. A later growth of silli- 
manite developed at about 45® to the banding. Note ])sammitic 
quartz-biotite bands. 
B. Sillimanite-biotite-plagioclase granulite. No tendency to 
orientation of any constituents. The clear areas arc fine granu- 
lar plagioclase. 
The fibrolite appears to be developing from biotite, the iron released 
in this change being represented by elongated grains of magnetit(' 
which occur most abundantly in the fibrolite layei’s. 
(ii) Sillimanite-biotite-plagioclase granulite (c.g., spec. 15078). Such 
I'ocks as these show’ the very interesting association of sillimanite 
with zoned plagioclase and myrmekite. In hand specimen the 
rock is tine-grained, greyish in colour ’with an irregular banded 
structure — fissile biotite bands alternating with granular quartz 
fels])ar bands. Under the microscope the structure is fine, even- 
gi’ained granoblastic w’ith lenticular areas rich in sillimanite and 
biotite with schistose structure. The approximate mineralogicaj 
