Preliminary Description of Coffinite-- a New Uranium Mineral

Phosphatian coffinite with rare earth elements and Ce-rich françoisite-(Nd) from sandstone beneath a natural fission reactor at Bangombé, Gabon

“…All of them, however, have concentrations of P exceeding 6.5 wt.% PzO5 with the highest recorded value of 8.9 wt.% P205. To calculate the number of ions in the coffinite formula unit (Table 1), we used the general formula USiO4-nH20 suggested by Smits (1989) and Janeczek (1991) rather than the formula U(SiOa).l-x(OH)4x proposed by the first investigators of coffinite (Stieff et al, 1956). From these calculations it follows that between 43 and 47% of Si is substituted by P. Calcium, REE and Pb have partially replaced U.…”

“…The observation that 47% of Si in coffinite is substituted by P clearly demonstrates that coffinite compositions may vary widely because of substitutions for both U and Si. The first investigators of coffinite reported As in their chemical analysis of impure material (Stieff et al, 1956). Arsenic may substitute for P; therefore, it is possible that As may also replace Si in coffinite.…”

Formation enthalpy of ThSiO4 and enthalpy of the thorite → huttonite phase transition

“…ThSiO 4 , and more often USiO 4 , often exist in nature with hydroxyl substitution Enthalpy of formation of thorite and huttonite del, 1953;Stieff et al, 1955;Zhabin and Kazakova, 1960;Liu, 1982) and in associations and inclusions with other minerals (e.g., Keller, 1963;Förster et al, 2000). Thus, stabilizing factors of ThSiO 4 in nature are high temperature, substitution of Th and Si by other elements and hydroxylation (Makarochkin, 1981;Lumpkin and Chakoumakos, 1988;Hansley and Fitzpatrick, 1989).…”

Synthesis and characterization of coffinite

“…Coffinite was first observed in the La Sal mine, Colorado Plateau [26], and was named after R.C. Coffin (American geologist, pioneer in the study of the uranium deposits in the Colorado Plateau).…”