Lokkaite, a new hydrous RE-carbonate from Pyörönmaa pegmatite in Kangasala, SW-Finland

Abstract

Lokkaite is a new RE-carbonate found in an old pegmatite quarry as a supergene mineral associated with tengerite. Electron microprobe analysis gave: Y-earths 48.7 %, Ce-earths 4.3 %, CaO 3.2 % and Fe2O3 0.4 %. Thermal decomposition gave: CO2 32.4 %, H2O+ 1.6 % and H2O- 5.4 %, total 96.0 %. When omitting Fe the analysis gives the formula Ca0.23RE1.58(CO2.87)3 • 1.58 H2O. Lokkaite is orthorhombic, the diffraction symbol is mmmB - - -; a0 = 39.07 Å, b0 = 6.079 Å and c0 = 9.19 Å. The mineral has a distinct superstructure. The dimensions of the sub-cell are: a'0 = ½a0, b’0 = b0 and c’0 = ½c0, and the diffraction symbol is mmmPb - -. The strongest X-ray powder lines of lokkaite are: 19.59 (35), 9.77 (50), 6.509 (55), 5.792 (45), 4.594 (75), 3.902 (60), 3.808 (100), 2.931 (40), 2.535 (35) and 2.045 (35). The colour is white, α = 1.569, ß = 1.592 and γ = 1.620. Elongation is positive and c // Z. The name lokkaite is in honour of the late Professor Lauri Lokka, former Chief Chemist of the Geological Survey of Finland, in recognition of his valuable contributions to the chemistry and mineralogy of the RE-pegmatites of Finland. The name was approved in advance of publication by the Commission on New Minerals and Mineral Names of the IMA.