Hobbies And Interests
Colors
Opals are made up of minute hydrated silica particles, chemical name SiO2(H20). The Manual of Mineralogy explains how the water content of between 2 and 20 percent allows light to be refracted through the particles. When the light changes intensity or direction, the refraction also changes and the opal appears to vary in color. As in water refracting to create a rainbow, all the colors and hues of the prism can be seen in this semi-precious stone.
World's Largest
Found in 1956, the Olympic Australis is the largest and most famous opal in the world. Weighing 3,450 grams and 17,000 carats, it is 11 inches long, 4¾ inches high and 4½ inches wide. It is on show at Altmann and Cherny's showroom in Melbourne, Australia, and is valued at 2,500,000 Australian dollars ($2,417,591 U.S. as of September 28, 2010).
Sources
Ninety-five per cent of the world's opals come from Australia, where it is the national gemstone, but the semiprecious gem is also mined in much smaller quantities in Mexico and Brazil.
Martian Prospects
It is possible that there will one day be mines much further afield than today.
The National Aeronautics and Space Administration reported in October, 2008, that a hydrated mineral very similar to opal had been found on Mars. NASA's Mars Reconnaissance Orbiter made the discovery while searching for water and possible life on the Red Planet.