The Granite Industry of Southwestern New Brunswick: A Historical ...

6 The Granite Industry of Southwestern New Brunswick: A Historical Perspective
Polished sample of Canada Pink. A coarse-grained,
medium pink granite from the Dawson Mountain
Quarry (Map 2, 44), showing pink potassium
feldspar, glassy quartz, white plagioclase feldspar
and flakes of dark biotite. JH
Polished sample of St. George Red. A mediumgrained,
deep pink, equigranular granite from one
of the Young quarries (Map 3, 33), showing red
potassium feldspar, glassy quartz, white plagioclase
feldspar (albite) and minor flakes of dark biotite. JH
veins and as veinlets and patches with
parallel extinction in crystals of orthoclase
and microcline. In some instances, crystals
of albite are continued as vein-shaped
bodies across the orthoclase.
The biotite is fresh in the lightcoloured
granite, partially altered in the
medium reds, and completely altered in
the deeper red varieties. The alteration
products are green chlorite, which retains
the pleochroic haloes, and in some
instances muscovite. Fluorite was observed
in one section, and iron ores are a common
accessory mineral. In some sections, there
is an appreciable amount of red iron oxide
in cracks and cleavage planes.
Imperfections in the red granite are
not common. These comprise occasional
rounded bodies up to four or five inches in
diameter with narrow gradational borders
against the granite. They are made up of
fine-grained grey rock and commonly show
phenocrysts of red feldspar in all sizes up to
one half of an inch or more across. Under
the microscope, the phenocrysts are seen
to consist of cores of cloudy and altered
orthoclase with rims of plagioclase.
The matrix is made up chiefly of
quartz, plagioclase and biotite. Quartz
occurs as distinct fragments or crystals
surrounded by secondary quartz in parallel
arrangement. The quartz also occurs as
large poikilitic crystals with irregular
boundaries, surrounding plagioclase and
biotite. The plagioclase in the matrix
is fairly clear and unaltered. Biotite is
quite fresh, showing incipient alteration
to greenish chlorite, and appears to lack
the pleochroic haloes that are so common
in the normal granite. The granite also
contains small lenses of pegmatite and
dykes of reddish aplite.
A microscopic study of the polished
surfaces on several granite specimens
in various shades of red reveals some
interesting facts. In the deep red stone,
the feldspar crystals have been very little
altered, and the crystal edges and angles are
sharp and clearly defined. The darkest red
samples also have feldspar aggregates of a
more or less uniform size.
In the lighter coloured granites,
alteration of the feldspar seems to be
more pronounced, and the feldspar masses
are more irregular in size. Thus, in the
light pink variety, the feldspar crystals
vary in size from less than one sixteenth
of an inch in diameter up to one half of
an inch or more, and the crystal edges
are not so clearly defined. The biotite