Mineral Industries and Geology of Certain Areas - Vermont Agency ...

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58 REPORT OF THE VERMONT STATE GEOLOGIST.
iorphic individuals bounded by prismatic and pinacoidal planes.
They are characterized by the development of a zonal structure,
with inclusions of the ground-mass stage in the outermost zone.
Plagioclase crystals are occasionally noted, not glassy but much
weathered. They are rare, however, and small. The biotite
does not differ in habit from that mineral in the granite. Irregular
grains of titanite and needles of apatite are found.
Touching the above, and at the sides of the V, is developed
the facies of the rock in which no hiotite is present. Hand
specimens show silvery scales of muscovite in great abundance,
making, with glassy feldspar and quartz, a very fine-grained
rock with no ground-mass.
Microscopical study reveals the presence of glassy microcline
as the predominant feldspar, with much less of plagioclase and
quartz, these last being in nearly equal amounts. A little orthoclase
is also present. Muscovite, in large patches and scaly
aggregates, is extraordinarily abundant. Magnetite and apatite
occur in large grains. Occasionally small pieces of pyrite
may he observed.
The extremely coarse-grained facies exhibits only biotite and
feldspar to the tinaideci eye. The biotite is in thin brownish
black leaves which are often 2 cm. in diameter. The feldspar
is bluish gray. It does not appear to be tvinned, and on its
flashing cleavage faces no striations can be detected. The single
pieces of massive feldspar are often 3 cm. across.
When viewed under the microscope the rock is seen to be
made up of microcline and hiotite. The feldspar is very generally
characterized by the usual delicate twinning lamellae of
microcline, and it is intergrown with quartz as in graphic granite.
The crystals of quartz are often .8 mm. in length. They
present triangular, spike-like, or more complicated forms..
They may be readily recognized by their interference colors as
compared with those of the feldspar, and they are large enough
to answer to tests with convergent light. They extinguish
simultaneously. Small crystals of plagioclase are also enclosed
4'
REPORT OF THE VERMONT STATE GEOLOGIST. 59
by the microcline. Much chlorite has resulted from the
weathered condition of the mica.
The granite industry at Barre, Vt., is of comparatively recent
development. As far back as 1833 blocks of stone were drawn
by ox teams to Montpelier to furnish the granite columns of the
capitol, but the period of active work on Millstone Hill dates
hack only a score of years. It was the order for ten million
paving blocks for the city of Troy which first stimulated activity
on the hill. Now 2,000 quarrvmen are engaged to work there.
The quarrying operations have been conducted with extraordinarv
energy and ability. Before the introduction of steel
hoisting machinery derrick sticks of wood, ninety feet in length,
were brought from Oregon. The most improved appliances
.are used in the shops at Barre for shaping the stone. The sheds
for working under cover at a nearly constant temperature summer
and winter are the largest in the world.
The gray granite of Barre is remarkable indeed for its evenness
and beauty in the rough and in polished pieces. Its qualities
of resisting the agencies of weathering, and of continuing
to look clean and bright after exposure, are greatly in its favor.
It has become famous as well for its wonderful adaptability to
tool treatment. On the singularly beautiful monumental stone
over the grave of the two Gobbi children in the cemetery to the
west of the city an armful of roses and lilies has been carved
in the round with matchless skill. Such work would have been
wonderful in marble. The monument to Robert Bur.ns in the
city of Barre, with its statue of the poet, and pedestal covered
by illustrative tablets, is probably the noblest piece of granite
carving to be found in any city.