Boulder opal ring in sterling silver is a simple design that makes a big statement in a larger size. This opal shows a unique pattern in the host rock, with different colors and rivers of blue, purple and white opal running throughout the stone like hidden streams. Boulder opals are cut from the opal's host rock which is most often ironstone. The opal deposits usually show up like rivers of color and shimmer within the stone. These are a very organic and natural-looking type of opal, resembling landscapes like this one, each one hand-painted by nature.