Hobbies And Interests
History
In 1849, fire opals were first discovered in Angaston, Southern Australia, by a German geologist named Johannes Menge. Slowly, the commercial mining of opals began in Australia, with specimens being sent to Europe for cutting, polishing and and sales. Because of their profitability, those that processed the stones moved some operations to Australia, and locals were hired to help. Charles Deane is famous for being among these early workers. This eventually led to Australians dominating both the mining and preparation of the stones. By 1932, European mines were no longer able to keep up with the influx of Australian stones into the market. Despite the industry's decline during the Depression that soon followed, Australia has been the leader in the world's fire opal production ever since.
Geography
Mining and production of fire opals is dominated by the state of Southern Australia, with the majority of opal fields being found in the Great Australian Basin portion of the state. The Great Australian Basin in a large geographic feature, covering 1.7 million km. The land in this area consists of hills and valleys, with deposits of opals being found only 20 to 30 meters below the surface. The towns of Coober Pedy, Mintabie and Andamooka are the major cities in the Great Australian Basin that produce opals.
Significance
There are approximately 223,000 square km of untapped fire opals in Southern Australia. It is estimated that the mining of these opals will draw $4.7 billion, indicating that fire opals will continue to be a valuable resource for the Australian economy. To consumers, opals also offer great investment potential. The highest-quality, rough-cut opals are priced at approximately $11,000 per karat, with average-quality, rough-cut opals fetching around $1,000 per karat.
Features
Australian fire opals differ from fire opals mined in other parts of the world, which are typically a solid orange, red, or amber color. Australian fire opals are typically solid-black opals with an array of vibrant colors visible on the surface of the gem. These colors can be any combination of shades, including reds, oranges, yellows, blues, greens and purples. These colors are the so-called "fire" of the opal. On Moh's hardness scale, fire opals register around 5.5, making them a semi-malleable stone. Their luster is classified as glassy or vitreous, and they fracture unevenly.
Classification
Fire opals are classified by a number of different factors, including body tone, play of color, brilliance, patterns and faults. In terms of body tone, the darker the fire opal, the more valuable it is considered. The play of color describes the extent to which all the colors of the full spectrum are represented in each stone, with stones showing distinction in all seven spectrum shades coming in at the highest values. "Brilliance" is a term used to apply to how brightly the fire of the opal shines when placed face up. Each fire opal has its own pattern of fire, and the pattern type contributes largely to the value of the stone; the more rare a particular pattern type, the more precious the opal. Faults are natural blemishes that occur on the surface of the opal, decreasing its value. Cracks, sand inclusion, gray surface lines and sections that lack color are all faults that can be found in fire opals.