Australia produces around 95% of the world's opal for use in the jewellery industry. There are lots of opal mining towns in Australia but only one is well known throughout the world: Coober Pedy.
The opal mining fields of Coober Pedy lie in the outback of South Australia, 750 km north of Adelaide. Many of the locals in Coober Pedy prefer to live underground in dugouts where it is cool in summer and warm in winter.
In 1995 Australia issued two stamps with opal holograms. When the stamp is held up to the light the hologram comes to life just like an opal and the color rolls and changes when you move the stamp.