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.
If you love the multi-coloured precious stones, don't forget to visit the opal shops in any mining town to see (and buy) beautiful opal jewellery. Opal is an unique Australian gemstone and a wonderful souvenir. Don't worry, small pendants are quite affordable.
Definitely April to late September is the best time for a trip to the opal fields. Summer is just too hot.
It is really a lovely drive from Winton down to Quilpie and Yowah. Take your time, and enjoy this true Outback experience.