cuff
buttons, scarf pins, hat pins, and other stones for less expensive
jewelry are thereby obtained. Some of this gem was found at
Yer-rington, Nev., during 1907.
BENITOITE.
Benitoite
is a new gem mineral from California from the Mount Diablo range near
the San Benito-Fresno county line. The gem has a blue color and was
first mistaken for sapphire when discovered early in 1906 by Messrs.
Hawkins and Sanders. The following notes are taken from a description
of the physical and chemical properties of the stone by Messrs. George
D. Louderback and Walter C. Bias-dale,3 and from a description of the geological occurrence by Ralph Arnold.6
Benitoite is regarded as an acid titano-silicate of barium with the formula BaTiSi309.
It fuses quietly to a transparent glass at about 3, the fusing point of
almandine garnet. Though practically insoluble in hydrochloric acid,
it is readily attacked by hydrofluoric acid and dissolves in fused
sodium carbonate. Its hardness is above 6,
probably
between 6-1/4 and 6-1/2, and its specific gravity is 3.64-3.65.
benitoite crystallizes in the hexagonal system, trigonal division. The
common forms observed are the basal plane, positive and negative
trigonal pyramids, and corresponding prisms. The common habit is
pyramidal, though occasionally the base is well developed and the
crystal tabular. No tendency toward a prismatic habit was observed. The
refractive index is a little above sapphire, or about 1.77 for the
ordinary ray and 1.80 for the extraordinary ray. The double refraction
is therefore strong. The color of benitoite varies from deep blue with
a violet tint to pure blue of a lighter shade; small crystals are
sometimes perfectly colorless. The color is not affected when the
mineral is raised to a red heat.
The
features of benitoite as a gem are its brilliancy, attractive colors,
and strong dichroism, and its hardness is nearly equal to that of
peridot or kunzite. The depth of color varies in different portions of
many of the crystals, while the strong dichroism causes a variation of
color depending on the direction the crystal is viewed. Light
transmitted perpendicularly to the base is practically colorless, while
that parallel to the base, or perpendicular-to the principal axis, is
blue. To secure the best effect, then, the gem should be cut with the
table parallel to the principal axis and not to the base, which is
contrary to the rule for sapphire.
Benitoite
occurs in veins and pockets or geodes in a lens of basic schist
inclosed in one of the largest serpentine areas of the Coast Range of
California. The mineral is associated with natrolite and a black or
brownish-black mineral, thought to be a new species and called
carlosite. The lens of schist inclosing the benitoite veins is about
150 feet wide and at least 1,200 feet long, and cuts through a low
serpentine hill with a strike of about N. 70° W. and a dip of 70° to
80° NE. The schist varies in color from dark greenish on the southwest
border to bluish in the immediate vicinity of the gem-bearing veins
near the middle of the mass. The bluish portion is an altered phase,
and is often largely replaced by natrolite in contact with the veins.
The altered portions of the schist are full of cracks
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