300 2 lie American Geologist. November, i9ui> 
less minerals, except certain oligoclases (which do not occur 
in the noryte), by the very large optic angle and the parallel 
extinction. Such sections are rectangular with rounded an- 
gles and negative elongation. 
The cordierite contains spherical and acicular liquid in- 
clusions, and particles of magnetite which are nearly always 
coated with a very thin layer of green spinel. But the most 
characteristic inclusions, which, when present, even serve to 
identify the cordierite, are minute short prisms of staurolite. 
They also serve to show the orientation of formless grains of 
cordierite. since the vertical axes of the two minerals are near- 
ly always parallel.* In spite of these numerous inclusions 
the cordierite shows no trace of the pleochroic halos u.^ually 
so common in this mineral. 
Quartz occurs in large granular masses enclosing the cor- 
dierite, biotite and bronzite. It shows no crystal outlines nor 
cleavages. It contains minute liquid and solid inclusions. 
Magnetite is usually in the form of very small rounded 
grains, widely, but sparsely, distributed. It occurs also as 'a 
fine dust. Crystal outline is very rare, and the grains are 
only occasionally large enough to give the characteristic blue- 
black metallic reflections. The mineral is often coated with 
a thin layer of green spinel. 
Pyritc is nearly always xenomorphic; it is occasionally as 
abundant as the magnetite. 
Staurolite occurs in extremely small microscopic prisms, 
often nearly as dark colored as biotite. The crystal form is 
nearly always well developed, and the outlines are usually 
rectangular. The faces observed are:/'(ooi), 5^^010), /i\ioo), 
and more rarely ^'(loi), and [;//(iio) (?)]. No twinning nor 
cleavage occurs. The color is a golden yellow with distinct 
pleochroism : 
«g = dark golden yellow. 
"m ^ yellow. 
;?p = pale yellow or colorless. 
The absorption is therefore »g > w^j > «p_ 
The refringence is very high, and the birefringence weak, 
only giving white and pale yellow. The elongation is positive 
with parallel extinction. 
*See further iinder staurolite. 
