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Aventurine
The name aventurine is applied to an ornamental
material consisting mainly of quartz. It is therefore described
here under this heading, although it is actually a metamorphic
rock, a quartzite, containing platelike crystals of other
minerals, usually green mica. It is also, improperly, called
Indian jade. It should not be confused with aventurine feldspar,
a red variety of albite.
Appearance Consisting as it does of minute,
juxtaposed grains, it is normally not transparent, but somewhat
turbid, Sometimes the green mica plates are obvious and greatly
influence the color, which may be an attractive, bright green.
More often, it is merely greenish off-white or grayish white.
The overall appearance can be quite similar to that of some
jadeite. It is generally cut into curved pieces for necklaces
or other jewels, or for use as pendants, but is also much
used for carving and figurines. Because of its heterogeneous
structure, it does not easily acquire a good polish.
Distinctive features The granular appearance,
the possible presence of distinct green fibers, and its particular
translucence are the most distinctive characteristics. Specimens
similar to jadeite jade are immediately distinguished by their
density. It is also much more brittle than jade.
Occurrence Aventurine comes mainly from India,
the Soviet Union, Brazil and Australia. but also from Germany.
It is also fashioned in all these countries.
Value Very modest, when, as is usually the
case, the material is whitish to grayish or dull green and
the workmanship is of a low level. But expertly fashioned,
bright green pieces are almost as valuable as true jades.
Simulants and synthetics Aventurine feldspar
is imitated by glass, usually m the form of a brown paste
containing golden metallic fibers, hence somewhat dissimilar
Some people, in fact, claim that the name aventurine was originally
given to a type of Murano glass containing metallic fibers
and only subsequently applied to the ornamental mineral which
looks (very vaguely) like it. It is not manufactured synthetically.
Because of its granular structure, minute discontinuities
and porosity, aventurine absorbs artificial colorants quite
easily, and consequently it is sometimes given a bright green
color, with a view to greatly increasing its value.
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