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PRECIOUS STONES.
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855
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dony
varies from translucent to opaque gray to yellow and yellowish green in
color. The chert is gray to yellowish and brown, and grades into
chalcedony. The variscite ranges from deep emerald or grass-green to
pale shades of green and to white. Wardite is green, bluish green, and
white, and is probably associated with other phosphates. The structure
of the different minerals in amatrice is nodular, concentric, oolitic,
and brecciated. These varieties of structure are not limited to one
mineral, but occur in the several minerals composing amatrice. The
variscite generally occurs in nodules in chert and chalcedony,
sometimes with an indistinct banding and gradation from deep green to
pale green and white. In places the variscite has been shattered and
recemented with seams of chalcedony, different colored variscite, or
other white phosphates. An oolitic texture is present in some of the
variscite and associated matrix. Much of the chalcedony and chert have
a typical nodular and concretionary structure, and in many cases an
agate-like banding. The dark color of some of the chert and the
limonite-stained breccia furnish a strong contrast with the light and
dark green and white variscite and associated minerals.
Part
of the variscite found in the "jade" cut has a deep,translucent green
color resembling jadeite, especially near the borders of the nodules.
The interior of the nodules generally has a lighter apple-green color,
and sometimes a gray or white core. The matrix adjoining the nodules
is chiefly dark brown and gray chert and chalcedony, though some have a
yellowish color. It is firmly attached to the nodules, so that gems
can be cut showing the strongly contrasting colors of the two. In size
the variscite nodules range from less than a quarter of an inch to
over an inch across.
The
amatrice from the' "cobweb cut" has a structure resembling that of
cobwebs or the markings on a turtle's back. This mottling is not
confined to the variscite, but is evident in the chert and chalcedony
matrix around the nodules. The appearance is due to a fracturing of the
first deposit of these minerals and the deposition of different kinds
of mineral, or the same mineral with different colors, in the
fractures. A typical turtleback variety of amatrice is composed of
light-green variscite in which a network of deep-green variscite has
been deposited. The amatrice in the "cobweb" cut occurs both in nodules
of yellowish and gray phosphatic minerals with chert and in irregular
cherty masses. The nodules, which may or may not carry variscite, range
up to several inches in diameter. Some of them are much stained with
limonite, as is the cherty matrix.
Some
of the gems from the "apple-blossom" cut display the effect of apple
blossoms among green leaves. This is due to the intimate association of
oolitic particles and nodules of green variscite and a white phosphate
mineral with chalcedony. In some specimens the chalcedony contains
small spots of purple which heighten the effect of blossoms. The
greater part of the solid variscite from this cut has a paler and less
pleasing color than that from the jade cut, and owes its beauty to the
combination with the other matrix. Masses of variscite and phosphate
minerals with chalcedony and chert, 2 or 3 feet across, are found in
the "apple-blossom" cut. Such masses are composed of large and small
concretions and nodules of variscite and the different associated
minerals.-
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