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142 GEOLOGY OF NEW YORK CITY
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limestone,
while irregular or minute particles appear in the gneisses and
granites. Many of the pyrite specimens repay examination with a
hand-glass of low power, as its characteristic crystallization is well
shown, while the crystals taken from the dolomite beds are not rarely
of considerable size and perfection.
At
1st Avenue and Kipp's Bay (Schernikow) pyritohedrons almost rounded by
channeled flutings (oscillation with cube), At 32d Street between 5th
and 6th Avenues, at a depth of forty-nine feet (A- S. Coffin),
quartzite was taken out coated with pyrite.
Pyroxene, a
mineral in composition allied to hornblende, but in the examples found
on the island quite often devoid of iron, where the colorless white
variety prevails. It is found in the limestone in flat, brittle,
striated crystals, at Inwood and the old quarries, and is exhibited in
groups with quartz, from the dolomite.
Green crystals occur, as at 56th Street, 6th and 7th Avenues, but they are very rare.
Pyrrhotite, magnetic sulphide of iron, in imbedded nests from the dolomite at the Kingsbridge Ship Canal.
Quartz, silica,
is naturally omnipresent, but not frequently of cabinet interest, being
usually massive. Crystals of great beauty and smoky in color are found
in the limestone groups, and amethystine tints have been noted
elsewhere, while many drusy incrustations are taken in pockets.
Terminated
crystals with crystallized oligoclase from 56th Street and Broadway,
smoky from Fort George, milky from 118th Street and Morningside Drive,
projecting crystals on granite at 181st Street and Harlem River, may be
mentioned. Under the building of the Title Guarantee and Trust Co. at
146 Broadway, at a depth of 175 feet, gold quartz was reported.
Ripidolite (Clinochlore),
a mineral of the chlorite family, a hydrous silicate of aluminum, iron,
and magnesium, is developed extensively in Westchester County, and
appears on Manhattan Island. From the Jerome Avenue quarry, in
green-blue plates; in green plated rosettes in quartz from 104th, 105th
Streets, and 5th Avenue; taken forty-four feet below curb at 12, 14
West 32d Street. (A. S. Coffin.)
Rutile, oxide
of titanium, not uncommon, saturates phlogopite in microscopic form,
and occurs in good crystals; channeled square prisms with scapolite and
prochlorite from Fort George; large crystals in the Bronx on Jerome
Avenue at 171st Street. Exquisite small crystals, splendent and
blood-red on edges in
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