Product Code : 4221 Stone Name : Natural Boulder Opal Gemstone Size : L-38 x B-17 x H-6 MM Weight : 38 Carats
Opal is Australia’s national gemstone, and it’s no wonder--approximately 97% of the world’s opal is discovered in Australia! There are 3 types of opal found in Australia: white opal, black opal, and boulder opal.
White opal is the most common type of opal found and it’s probably what you picture when you hear the word ‘opal.’ Black opal, on average, is the most expensive type of opal; however, boulder opal is undoubtedly the most interesting.
Boulder opal is the only type of opal in which every stone is one-of-a-kind, making it truly unique. It can be found in every color in the rainbow and is only found in the most remote part of Australia’s outback, central Queensland.
Boulder opal earned its name because the stones form in the shape of a boulder. The boulder can be as small as a fist or as large as a person. Ironstone is the dark “host rock” that opal attaches to in boulder opal. The opal within the ironstone forms over millions of years from silica deposits that trickle via water through the stone.
Because the opalization process depends essentially on water, silica, and the patterns they eventually create in the host rock, the different boulder fields produce equally different boulder opal with varying properties. For example, the opals found in Yowah are referred to as Yowah nuts because the color forms in a circular shape, creating an opal that resembles a little nut. In other boulder opal fields, such as Winton or Opalton, the color within opal can form as specks, veins, flashes or solid color.