Home > American Minerals II – April 7 > MS1554 Clarkeite replacing Uraninite

Clarkeite replacing Uraninite - Sold

Clarkeite is a hydrous sodium uranium oxide. Ross et al. (1931) named the mineral in honor of Frank Wigglesworth Clarke (1847-1931), geochemist at the United States Geological Survey. Clarkeite forms by oxidation of uraninite. Synthesis temperatures (Gruner, 1954) and textural relations (Ross et al., 1931) indicate that clarkeite forms during the final stages of pegmatite crystallization and not by subsequent weathering by meteoric waters. Finch & Ewing (1997) matched the powder X-ray diffraction pattern of clarkeite with chemically similar synthetics, from which they derived and refined a structural model using Rietveld methods. Finch & Ewing (1997) concluded that clarkeite has hexagonal (rhombohedral) symmetry and proposed its currently accepted ideal formula: Na(UO2)O(OH)·nH2O.

Popularly known as gummite, these specimens are now known to consist mainly of clarkeite. Clarkeite forms a waxy orange halo around an eye of unaltered black uraninite, 6 mm across. Individual clarkeite crystals are too small to see with an optical microscope; clarkeite is crypto-crystalline. Although crude, the cubic form of the original uraninite crystal is still evident. Minor mica and feldspar are attached.