Geology in Pop Culture
Released in 1990, The Rescuers Down Under continues the escapades started in 1977's The Rescuers. However, in this adventure our favorite mice, Bernard and Bianca, travel down to the Australian outback (not the steakhouse). Here, they find that the villain of the story, the poacher Percival C. McLeach has kidnapped a boy, Cody, while hiding out in some abandoned opal mines.
So what exactly is opal anyway?
Opal (SiO2.H2O) is a mineral that forms from the packed spheres of silica (SiO2), also known as the mineral quartz. Opal is a hydrated form of silica where water has been shown to include between 3 and 9% of the total mineral structure. Unlike many minerals, because of how it is formed, opal is amorphous, or without form. This means that there is no crystal structure or cleavage that is seen in most other minerals. Opal forms through the processes of solidification of gelatinous or liquid silica within cracks and voids of other rocks.
Since the opals are created by spheres of silica and water, the size of the sphere's dictates the colors that are produced. These colors are refracted through the opal like a prism, with larger spheres yielding red or orange, and smaller ones radiating blue. However, this is only the case with precious opals, the more gem quality ones. Most opals, ~95%, are referred to as common opals. These are opals that do not have the "play-of-color" expected in opals as seen in the image above. Although still beautiful, they are harder to identify than the precious opals.
