Jasper
is opaque, fine-grained or dense variety of the silica mineral chert.
Jasper, long used for jewelry and ornamentation, has a dull lustre but
takes a fine polish. Its hardness and other physical properties are
those of quartz.
In ancient writings the term jasper was chiefly applied to translucent and brightly colored stones, particularly
chalcedony, but also was applied to the opaque jasper.
Jasper was known as the great "rain-bringer" in the fourth century.
For thousands of years, black jasper was used to test gold-silver alloys
for their gold content. Rubbing the alloys on the stone, called a
touchstone, produces a streak the color of which determines the gold
content within one part in one hundred.
Jasper is one of the gemstones, that used in
commesso, also
called florentine mosaic. Commesso is a technique of fashioning pictures
with thin, cut-to-shape pieces of brightly colored, semiprecious
stones, developed in Florence in the late 16th century. The stones most
commonly used are
agates,
quartzes,
chalcedonies,
jaspers, granites, porphyries, petrified woods, and
lapis lazuli. Commesso pictures, used mainly for tabletops and small wall panels, range from emblematic and floral subjects to landscapes.
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