of
the most conspicuous and extraordinary of the island's minerals. It is
sometimes beautifully shown in stars of radiating black crystals; large
splendent crystals occur in the quartz of the granite veins, the most
phenomenal of which is the one figured, discovered by Mr. Niven at
171st Street and (Fig. 34) Fort Washington Avenue, while radiating
groups of considerable size offer the collectors admirable and almost
brilliant specimens. The tourmalines are very commonly, if of some
dimensions, broken or faulted, viz., split and thrown sideways, and the intervals filled in with quartz or feldspar.
Mr.
Chamberlin uncovered the really remarkable deposit of iron (black)
tourmaline, " in a vein of gray quartz traversing gneiss, parallel to
the stilbite veins near the Fourth Avenue tunnel, above 96th Street."
These crystals were of high grade, terminated and brilliant. Tourmaline
in places becomes a rock ingredient and forms a gneiss.
Triphylite, phosphate of lithium, iron, and manganese; reported.
Tremolite, white-bladed or needle-formed amphibole; at the ioth Avenue serpentine locality; in dolomite.
Uraninite, oxides of uranium, with lead, thorium, etc.; reported.
Vermiculite, near jefferisite, a hydrous, micaceous mineral spurting out, when heated, worm-like ribbons; reported.
Vivianite, phosphate of iron, dichroic and usually, to the eye, blue; reported.
Wad, see manganese oxides.
Washingtonite, see menaccanite.
Water, chalybeate
(iron) waters reported; many wells have been sunk on the island; one
reported to the author sunk 432 feet yielded 1,200 to 1,500 barrels a
day, two others driven to depths of 1,001 and 1,500 feet yielded
nothing.
Wollastonite, silicate of lime; reported.
Xenotime, Monazite, and Zircon, the
first two phosphates of rare earths (Cerium, yttrium, erbium,
lanthanum, didymium), and the last silicate of zirconium, have been
found by Mr. Wm. Niven in the prolific locality at Washington Heights,
and occurred in three pockets very near each other in a vein of coarse
granite made up of granular quartz, orthoclase, and " flaky muscovite."
These minerals are translucent brown in colors, small, but of
exceedingly great interest. Another mineral which the prospecting
instructor may notice occurs in clusters of hair-like blue needles,
sometimes in single blades, and is found in feldspar.
