In Lightning Ridge we visited the “Walk-in Opal mine”. The mine was closed some years ago when the owner passed away. The current owner opened the mine for tourists. 
Opal is a form of microscopic crystallized quarts. It is formed by leached out quarts trickling down into the clay layer below. Over time it filled up gaps and very slowly crystalized due to evaporation of the water. Some opal has up to 10% water still in it. This all happens in a dry desert type enviroment. Not like other large quarts crystal which are formed much deeper in the earth crust. The colorful reflections in opal come from the many small invisible microscopic Crystal surfaces in the solidified droplet/sfeer. The 1 m clay layer is some 10 – 50m underground. It is soft and can be dug up with a pickax. Prospectors can lay a claim on a 50×50 m land plot for A$800 per year. They drill/hack a small shaft and then tunnel through the clay layer searching for the nuggets of opal. If they are lucky they find some but mostly the takings are small and only small fragments of larger “sfeers” are found. It is a mom and pop mining industry. Lightning Ridge is full of people looking for their fortune. Jamaliah made the shop owner happy by buying a ring with a 9 carat opal (mother’s day present).