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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.
To keep this mineral when in crystals from crumbling upon exposure it may be dipped in a thin mastic varnish or in a gum-arabic solution. Heulandite. This rare mineral has been found under the same conditions as laumonite in Shaft No. 2, but it is seldom to be met with, and then in small crystals. It is of a pure white color, sometimes transparent.
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.
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