32 No. 5
The Stone that Came in from the Cold
The first stamp depicting cryolite, a rare mineral whose name is derived from the Greek terms for “cold” and “stone” and is composed mainly of sodium hexafluoroaluminate (Na3AlF6), was issued in Greenland on 19 October 2009. It is a belated but fitting tribute to a mineral that played a fundamental role in the development of the world’s modern aluminum industry. Commercial mining of a huge deposit of cryolite found in the town of Ivittuut near the southwestern tip of Greenland started in the late 1850s and continued for more than a century even though the massive amounts of cryolite needed by the aluminum industry led over time to the invention of several processes for making synthetic cryolite. A whopping 3.7 million tonnes of the snow-white mineral had been extracted from the Ivittuut mine by the time it shut down in 1987!
In any event, cryolite’s claim to fame was attained in 1886, when Charles Martin Hall in the United States and Paul Héroult in France independently (and almost simultaneously) discovered that it could be used as a flux in the industrial production of aluminum. The large-scale electrolysis of purified alumina (Al2O3), which has a melting point of about 2000 °C, was prohibitively expensive until then, but the use of cryolite lowered the melting point of the mixture to about 900 °C and rendered the so-called Hall-Héroult process economically viable. Aluminum was on its way to quickly becoming the most widely used nonferrous metal in the world, with applications ranging from construction and the aerospace industry to the manufacture of cooking utensils and packaging materials.
Written by Daniel Rabinovich <[email protected]>.
last modified 8 September 2010.
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