Lightning Ridge, Australia Black Opal Mining Underground Geology
Opal is currently being mined from depths between 1 metre (3 feet) and 30 metres (90 feet) below the surface. The opal is found in sedimentary rocks. There are more than 200 distinct opal fields on the ridges of Cretaceous rocks surrounding the town of Lightning Ridge.
Opals are found in fault lines and in blows (side view)
Can you see the fault line below?