About Boulder Opal - History and Introduction
Boulder opal is one of the most valuable varieties of opal,
second only to Australia’s black opal.
Fine specimens of boulder opal can exhibit all of the spectral colors
through their distinct play of color.
Boulder opal may be considered to be less valuable than black opal,
but it is actually much rarer.
Boulder opal accounts for approximately 2% of all of Australia’s opal,
black opal equates to around 8% of the entire yield.
The remaining 90% is common opal,
often referred to as ‘potch’ or ‘white opal’.
Boulder opal is found embedded in large boulders of ironstone,
which is how it earned its name.
Occurring as pebble rock,
precious opal develops within thin veins,
fissures and hollows.
As opal miners attempt to remove the embedded opal from the ironstone,
some of the host matrix is preserved during the process.
For this reason, boulder opal is sometimes referred to as ‘opal in matrix’.
but ‘opal in matrix’
is a a generic term that can be used to refer to opal
from all around the world,
while the name ‘boulder opal’
is reserved only for Australian material.