has
pointed out, the entire lack of such a compound, considering the
frequent association of the oxides in the same formation, is striking.
Aside
from these general considerations bearing on its chemical character,
the symmetry and physical constants of benitoite do not appear to the
writer to indicate any close relation to beryl.
Benitoite as a Gem.
Benitoite
forms a beautiful gem stone, but only a small proportion of the
crystals are suitable for cutting. It is generally cut as a brilliant
to bring out both its color and the brilliancy and lire due to its high
refractive powrer. The deep violet-tinted blue of the finer
stones is very attractive and by many it is considered more beautiful
than that of the sapphire, which it distinctly surpasses in fire and
brilliancy. The color varies from colorless to very deep blue, the two
extremes being the least common. The finest stones are those with a
moderately deep color. Considerable judgment has to be used in getting
the proper attitude and proportions to bring out the full color-value
while preserving the brilliancy. Both color and brilliancy vary
materially in different directions and the color is often distributed
unevenly or zonally. Quite a number of stones which have been cut by
various lapidaries do scant justice to the possibilities of the gem. A
common result is the production of a sort of dull leaden, or in the
darker varieties blackish appearance.
The
large stones have a general run from a carat and a half to about two
carats, only a few exceeding the latter value. The largest flawless gem
yet obtained weighed a little over seven and a half carats when first
cut, though it has since been repolished and brought down to a little
below this value. It has a moderately deep blue color and is about
14.5 mm. long, 10.5 mm. wide at the girdle, and 8 mm. deep. It is the
property of Mr. G. Eaeret of San Francisco. This stone is remarkable in
that it is about three times as heavy as the next largest flawless
stone so far obtained, and also that it was found in the early days of
the mine almost at the surface. It is shown actual size in plate 33,
figures 1-4.
