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While
deposits of precious opal, apparently in
volcanic rocks, have been known in Indonesia
for a generation or more, little is known
of the deposits and the opal itself is not
well known beyond the country of its origin.
A short report on this opal is given by
Lambert and Brown (R1625).
They state that opal is known from three
localities, in western Java, western Sumatra,
and southwestern Sulawesi. Commercial production
only comes from the first of these areas,
the Labak district. The opal is largely
a 'jelly' type, but frequently shows excellent
play of colours.
The opal is mined by hand, the workers digging
holes in the layers of sedimentary and volcanic
sequences in the search for the sporadic
opal-filled cavities. The opal is thought
to have been formed during weathering processes
subsequent to the deposition of the sedimentary-volcanic
sequence.
The production is apparently sufficient
to supply a substantial local demand, especially
from tourists.
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