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After a long boiling with nitric acid it gelatinizes, but it foams up and fuses to a transparent glass before the blowpipe. A little stilbite may often be found on the dumps. Laumonite occurs in very small quantities on calcite or apopholite, and can hardly be expected to be found on the trip; but as it might be found, I will detail some of its characteristics.
They resemble each other very much; the iron pyrites, however, is in cubical forms and having the great hardness of from 6 to 7, while the copper pyrites, less abundant and in forms having triangles for bases, but having sometimes other forms and a hardness of but 3 to 4. Both are similar in aspect to a piece of brass, and cannot be mistaken for any other mineral. Stilbite.
Natrolite resembles stilbite, but may be distinguished by gelatinizing readily with hydrochloric acid and by not intumescing when heated before the blowpipe; from the other minerals by the form of the crystals and their setting, also the locality in the tunnel in which it was found.
Among them the species Analcime, Stilbite, Natrolite, and Chabazite may be mentioned as of most common occurrence. The microscope has shown that pure quartz is oftener present in lavas than was formerly supposed.
Heulandite is distinguished from stilbite by its crystals and perfect solubility; from apopholite by form of crystals. In the next part of this paper I will commence with Staten Island. July 1, 1882.
Volcanic ash, or bole, is frequently found separating the different lava-flows; and in the upper amygdaloidal sheets numerous secondary minerals are found, such as quartz, agate and jasper, stilbite and chlorite. The total thickness of the whole series, where complete, is about 6,000 feet, divided as follows: 1. Upper trap; with ash and inter-trappean beds 1,500 feet 2.
Copper pyrites, by its aspect from the other minerals, and from iron pyrites by its inferior hardness and less gravity. Stilbite is characterized by its form, difficult gelatinizing, and intumescence before the blowpipe; from natrolite as mentioned under that species. Laumonite is known by its generally chalky appearance and a probable failure in finding it.
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