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GEMS AND PRECIOUS STONES. 897
quartz-albite
rock characterized by numerous wavy bands of brownish-red garnets.
These bands lie nearly horizontal in their general trend, being
parallel to the slight dip of the dike. The " bottom rock" is likewise
free from gem stones, but both it and the "top rock" are of great
interest from the scientific point of view. Between* the " top rock "
and the " bottom rock'' is the middle portion, called the " pay streak
" by the miners, in which the gem minerals of value are found. Here
also occur the cavities or pockets which often yield an abundance of
the well-crystallized minerals shown in the exhibit.
The
top horizontal shelf on the south side of the exhibit case contains
the granitic and gabbro country rock, and also the partly altered
gabbro—a loose, friable rock—and the completely altered gabbro, which
as a brown iron-stained clay has been washed into the cracks and seams
of the pegmatite rock. Where such a crack extends into a pocket the
clay has coated the gems and associated minerals found therein. There
are shown, for example, white feldspars of the pegmatite coated with
the brown clay derived from the gabbro country rock. The origin of the
clay of the gem pockets is thus explained.
The
second horizontal shelf on the south side contains different varieties
of the "top rock," consisting of graphic pegmatite and granular
pegmatite. The third horizontal shelf shows the mineral aggregates of
the middle part or " pay streak," which yields on decomposition the
loose, friable material forming the gem pockets. This same shelf also
shows examples of the banded " bottom rock." '
The
sloping shelf on the south side contains large specimens of the
different varieties of the pegmatite rock, including granular, graphic,
and banded pegmatites. Several of these larger specimens have been
sawed and polished and are well adapted for use as an ornamental stone,
especially when cut obliquely so as to form wavy lines and circular
effects resembling bird's-eye wood. One specimen in particular consists
of a large section of the entire pegmatite dike and shows the aggregate
of lithium minerals in the upper portion or " top rock," the granular
pegmatite of the middle portion, and the banded "bottom rock."
The
sloping shelf on the north side of the case illustrates the mineral
contents of the gem pockets. A sample of the gem-bearing clay or pocket
material is first shown, below which is an equal amount of similar gem
clay separated into its constituent minerals; thus the relative
proportions of the gem tourmaline, the clay washed into the pocket from
the decomposed gabbro country rock, and the various minerals associated
with the gem tourmaline are exhibited. For example, the pocket material
from the Tourmaline King mine, at Pala, shows much lepidolite,
orthoclase, clay, and gem tourmaline (pink and green), and smaller
amounts of muscovite and quartz. Similar gem-bearing clay from the
Tourmaline Queen mine, at Pala, shows in addition to much pink
tourmaline, large amounts of clay, quartz, albite, and cookeite, but
practically no orthoclase. A gem pocket from the Ed. Fletcher, jr.,
mine, at Pala, shows in addition to much pink tourmaline, clay, and
albite, a considerable amount of lepidolite, with only a little
orthoclase. A gem pocket from the Pala Chief mine, at Pala, shows
considerable gem kunzite, with lepidolite, quartz, clay, cookeite, and
orthoclase, and smaller amounts
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