Boulder Pipe crystal opal, only small percentage boulder
opal forms as pipes and most is crystal opal and as the name suggests, the opal
is formed in pipe shape tubular holes when formed in the mother rock,
Pipe opal forms in running lengths in the sandstone potch in
single line or multiple fragments.
The darker the sandstone the darker is the opal colour.
If the opal cutter cuts
away the potch of the opal could be lighter and translucent, so most opals have
potch or sandstone covering sides and bottom.
Large pieces crystal opal do have striking patterns and most people would not realize the opal is
The pipe opal can be solid or tubular and when tubular with
hole it is sometimes confused with belemnite opals.