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_To Distinguish the Minerals together the one from the other_.--Calcite
by effervescing on placing a drop of acid upon it. 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.
Pectolite sometimes resembles some of the others, but may be readily
distinguished by its _tough_ long fibers, not brittle like natrolite.
Datholite may generally be distinguished by the form of its crystals and
their glassy appearance, with great hardness, and by tingeing the flame
from the blowpipe of a true green color. Apopholite is distinguished
from calcite, as noticed under that species, and from the others by its
form, difficult fusibility, and part solubility.
Phrenite is characterized by its hardness, greenish color, occurrence,
and action of acid. Iron pyrites is always known by its brassy metallic
aspect and great hardness. 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.
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