Gemstone necklace with an Australian boulder opal ~ including 2mm leather cord in antique brown, for knotting to desired length. Origin of the Boulder Opal "The boulder opal originates from the Queensland region of Australia. More specifically, the boulder opal is found in southwest Queensland, specifically in Quilpie, Yowah, and Eromanga. The sedimentary rock in this region dates back to the Cretaceous period. The rock thus dates back to a time that began around 145 million years ago with the end of the Jurassic period and ended about 66 million years ago with the beginning of the Paleogene period. Over time, weathering processes—well into the Tertiary period—released silica from the marine mud and its microorganisms, which was deposited in the impermeable cracks and crevices of the rock. The constant changes in humidity and subsequent evaporation ultimately led to the solidification of the silica, thus creating the beautiful opal. We hope you enjoy browsing our shop. If you like what you see, we would be very happy if you would follow us here :) "A stone is the condensed history of the universe" ~Art of Nature Berlin~