New Mexico Mineral Symposium — Abstracts

A hydrous rare earth copper arsenate mineral of the agardite group occurs as green needles in cavities of fluorite-rich rock from the Red Cloud district, Gallinas Mountains, N.M. The mineral was first recognized by Ramon DeMark, and its identity as an agardite—group mineral was confirmed via X—ray powder diffraction by Bob North of the New Mexico Bureau of Mines.

The general formula for minerals in the agardite group is Cu₆R(As0₄)3(OH)₆.3H₂O. Three members were previously known, in which R dominantly bismuth (mixite), yttrium (agardite), or aluminum (goudeyite). Previously analyzed specimens of agardite from Bou—Skour, Morocco and other locations contained dominantly yttrium plus lesser amounts of the rare earth elements and calcium. Microprobe analysis of the agardite from the Red Cloud district, however, shows that it contains calcium, aluminum, silicon, and rare earth elements as the dominant components, with only a trace of yttrium. Lanthanum and cerium are the most abundant rare earths in the agardite, with lesser amounts of praseodymium, neodymium, gadolinium, and samarium. The empirical formula of agardite from the Red Cloud fluorite mine is (assuming the water content to be stoichiometric):

Cu₅.₆₃Fe.₀₃Ca.₄₄Al.₂₅La.₂₃Ce.₁₈Pr.₀₄Nd.₀₃Sm.₀₁Gd.₀₂Y.₀₂Pb.₀₃Ba.₀₂Si.₁₉(AsO₄)_2.88(OH,O)₆.3H₂O

The rare—earth fluorocarbonate, bastnaesite, (Ce,La)CO₃F from the fluorite mine contains dominantly cerium and lanthanum (with Ce slightly > La) plus about 4-5 wt. % Pr₂O₃, 3% Nd₂O_3, 3% Gd₂O₃ and 0.5% Sm₂ O₃. Fluorite from the mine contains just a trace of yttrium (0.00 to 0.10 wt. 7. Y₂0₃), with apparently up to a few hundredths of a percent of lanthanum and cerium oxides. The low yttrium content is in contrast to that of green fluorite from the Globe pegmatite, Rio Arriba Co., N.M., which contains up to about 0.9 wt. % Y₂O₃.