times
red, gray, or yellow. It is sometimes transparent, and sometimes
opaque. It resembles the beryl and emerald ; its specific weight is
from 3 to 3'235. In some specimens, especially in the white variety, a
bluish opal tint is observed in the direction of the vertical axis.
It
is fragile. Some are phosphorescent in heat, others become electrical
by friction. This substance does not melt under the action of the
blow-pipe, excepting at its extreme edge. It dissolves slowly in
nitric acid, without effervescence. On account of the phosphoric acid
which it contains when solid, it is very useful as a manure.
Apatite
is generally found in primitive rocks, traversing granite, serpent
marble, and in the rocks of the spent volcanoes in Saxony, England,
Switzerland, Norway, and many American countries, where there is a
great trade in it as a material for enriching land.
Asparagine, which is a yellowish, translucent variety of apatite, is found in Estremadura.
