In 1954 J. P. Girault identified as britholite an occurrence of a thorium-bearing cerian silicate apatite mineral from Oka, Quebec. The unique composition of the Oka mineral, distinguished by P2O5>SiO2 in contrast to other analyses of britholite where silica greatly exceeds phosphorus pentoxide, suggests that the Oka mineral is an intermediate member of a series from britholite to apatite. The values of the physical properties of the Oka mineral approximate the average of those for britholite and apatite and lend support to this theory. An appreciable amount of thorium oxide, 5.62 per cent, is present in the Oka mineral. Britholite was originally found in the Julianehaab district of South Greenland. Recently several occurrences in the U.S.S.R. have been described. The Oka mineral is clove brown, massive, and has a dull resinous luster. The measured specific gravity of a concentrate of this mineral is 3.86 and the calculated value is 3.95. The higher index of refracton ω is 1.72. The Oka mineral is hexagonal with a = 9.48 Å and c = 6.96 Å (ignited material). The possible space groups are P63 or P63/m.
An accurate ion exchange separation technique was developed by using Dowex 50W-X8 cation exchange resin (50-100 mesh) and was applied to the quantitative separation of rare earths from phosphates, common elements and thorium all of which are present in the Oka mineral.
The physical and chemical data thus obtained indicate that the probable formula is: (Ca, Ce etc., Th, Mg, Fe, Na, Ti)5[(P, Si, Al)O43(OH, F) which is similar to the theoretical formula proposed by Machatschki in 1939 for britholite.