140 GEOLOGY OF NEW YORK CITY
NXtrolite, hydrated
silicate of aluminum and sodium, " in delicate, snow-white globes of
radiated, acicular crystals. Associated with chlorite, sphene, and
rutile at the brown calcite locality. Fifth Avenue and 104th Street"
(Chamberlin).
Necronite, a
fetid feldspar, originally found in limestone near Baltimore; taken on
Manhattan Island, " of a bluish white color in tabular masses in
limestone at Kingsbridge " (Chamberlin).
Oligoclase, a
feldspar, a silicate of aluminum, calcium, and sodium; generally
greenish, and under magnification showing repeated striae (twinning)
like ruled lines. Common; crystallized in well-developed crystals at
147th Street and Amsterdam Avenue, in solid quartz. Large crystals
from 134th Street and Amsterdam Avenue, and on Broadway (F. A. Camp).
Orthite, a
silicate of rare bases, the cerium and yttrium metals; usually applied
to the thin, straight, or curved crystals, a variety which readily
undergoes alteration. The crystals on Manhattan are dark, reddish brown
to black, frequently bent, and have been taken in oligoclase granite at
56th Street and Broadway, from two and a half to three inches in
length, and looking like thin rusty nails in the rock.
Orthoclase, silicate
of potassium and aluminum, common feldspar. This feldspar is found over
the island in a number of different aspects. It occurs disseminated in
white grains or more compact particles in the various gneisses; it
forms very pretty crystallizations over the face of the gneiss, often
in conjunction with epidote, while at the famous and prolific locality
at Fort George handsome examples have been extracted, and generally,
in the coarse veins of granite, cleavage plates of delicate flesh-tone
are obtained with sometimes lustrous reflecting beauty. It ranges in
color from white to red. Graphic mixtures of orthoclase and quartz
occur.
Chamberlin
has remarked of its occurrence on Manhattan Island: " Conspicuous
masses are not so common, and the collector needs to avail himself of
good opportunities for securing fine specimens of either the laminated
plates or crystallized fragments. The feldspar varies in color from a
dull white through different shades of yellow and flesh-color to a
bright red. Some of the localities were the following:
In broad flesh-colored plates with highly lustrous surfaces, 96th Street and 4th Avenue; 56th Street, 6th and 7th Avenues.
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