Boulder Opal

In simple words, Boulder Opal is opal and rock. It forms in voids and cracks within weathered ironstone boulders in Outback Queensland, hence the name. It appears as "seam" and "matrix" opals, or "nuts", like the famous Yowah nut.
This kind of precious opal displays the same brilliance and play of colours than the much better known black opals.
The opal veins and layers in the ironstone are usually so thin that boulder opals need to remain on its ironstone host.

The stone forms a natural backing which gives boulder opals a wide variety in shapes. This shouldn't be confused with opal doublets, which are man-made and somewhat artificial.

Don't think that these unique gemstones have no value. On the contrary! They come second after black opal in the ranking of Australia's precious opals. Due to the dark ironstone backing these opals have a dark body tone and a vibrancy of colours similar to black opal.

First discovered on a station south of Quilpie in 1872, boulder opals are found in a belt stretching from Quilpie to Winton in Outback Queensland.
Geologically known as the Winton formation, these sedimentary rocks formed in the Cretaceous period.

Apart from opal, the sediments also contain a rich source of dinosaur fossils.

Opal mining fields in Queensland

• Winton - The town is famous for being the birthplace of Waltzing Matilda, but also home of boulder matrix, a rare form of opal. Small streams of opal run throughout the ironstone and form interesting stones.
  Winton is a lovely Outback town that offers visitors a wide range of facilities.
• Opalton - The first opal was discovered in 1894, and Opalton soon became a bustling township. In 1899 the largest piece of opal, a pipe opal more than 3 metres long, was mined here. Today the township is much smaller. Try your luck in the public fossicking area. Meet the locals in the shop on any Thursday when they are waiting for their mail.
  A campground and basic cabins are available.