Brownish gray variety resembling perthite, 43d Street, 2d and 3d Avenues.
Red, 4th Avenue and 120th Street.
Cream-colored, 46th Street and 2d Avenue.
White, 94th Street and 3d Avenue.
White, slightly opaline, Harlem Tunnel.
Crystals are usually of the primitive rhombic form found lining fissures in gneiss.
Good
examples were obtained at 96th Street and 4th Avenue, 56th Street and
6th and 7th Avenues, and Lexington Avenue and 44th Street.
More
highly modified forms and larger in size usually appear in granite
veins. A few handsome specimens (in collection of Geo. F. Kunz), among
which was a remarkable twinned crystal, were found at Fort George; also
at 43d Street and ist Avenue. At the latter locality the feldspar of
the granite vein was changing to kaolin. The mica and beryls present
partook of the change. The orthoclase crystals were of large size, some
six by four inches. Crystals of less size appear in a porphyritic rock
on the east bank of the Harlem River above McComb's bridge (L. Winslow).
Remarkably fine groups of modified crystals coated with albite (G. J. Brush) were secured at 96th Street near 3d Avenue."
Phacolite, variety
of chabazite, distinguished by flatness or psuedo-hexagonal form from
twinning. Very rare. Reported from 43d Street and East River.
Phlogopite, magnesia
mica, is distinguishable by its golden brown colors and can be usually
recognized from its invariable association with limestone, in which it
is sprinkled. Where the dolomite becomes schistose, cleavable, and
merges into the gneiss rock, the phlogopite bridges over the transition.
PiNiTE, from iolite, by alteration, through hydration and solution.
Pyrallolite, under pyroxene; an alteration product; occurs in Finland in limestone; reported from the dolomite at Kings-bridge.
Pyrite, sulphide
of iron, the common yellow " fool's gold," is of frequent occurrence,
sometimes appearing as a brilliant crust of microscopic crystals over
rock surfaces, and again in nests in
