that
too pre-eminently esteemed—in which effects of this kind are produced
by the presence of little crystals of quartz scattered through the
mass, and reflecting the light on all sides. This last variety has
generally a very clear tint of greenish-white, or sometimes of a
reddish-brown.
The
aventurine with mica was formerly brought from the borders of the White
Sea; but at present it is furnished by Silesia, Bohemia, Siberia, and
France. The species with crystals comes from Spain, and has for some
years been produced by Scotland also.
Many
substances are sold in commerce under the name of aventurine that
produce similar effects, but are quite different in composition,
particularly certain varieties of felspar, filled with flaws and
minute fissures.
SECOND SECTION.
Before commencing the study of the stones comprised in this section, it is necessary to make an important remark.
So far the stones that we have examined are crystallized, and
nearly always anhydrous. It is quite otherwise with those that are to
be described in this group. They show no indication of
crystallization, and nearly always contain water.
It is probable that their elements have never
