Buy Yowah Opal Pre Drilled Online Direct From The Mines At Wholesale Prices. Opal Auctions has the largest selection of Yowah Opal online with over 10,000 pieces.Yowah opal is famous for its Yowah Nuts. They look like brown nobbies and have to be snipped to show if there is any opal colour in them. There is very little of this rough available most of the time. Yowah nuts are formed naturally in siliceous ironstone nodules generally referred to as a Yowah Nut. Yowah Opal fields are mostly worked by hand rather than by machinery and many Yowah Nuts are found by fossicking. A few open-cut mines have recently opened up large-scale opal mining. The Yowah Opal Festival is held mid-July and includes a jewelry competition.