Clarkeite
Clarkeite is a uranium oxide mineral of composition 223 or O·0-1H2O.
The color of samples varies from dark brown to reddish orange. Clarkeite forms by oxidation and replacement of uraninite late during pegmatite crystallization. Although uraninite-bearing granite pegmatites are common, clarkeite is rare and occurs intimately intergrown with other uranium minerals.
It is known from only two localities; the Spruce Pine pegmatite district in western North Carolina, US, and Rajputana, in the Ajmer district, India. Clarkeite is the only known naturally occurring high-temperature uranate. The general formula for ideal clarkeite is Na0-1.
It was named for Frank Wigglesworth Clarke, American mineral chemist, and former chief chemist of the United States Geological Survey.
