The rare earth-bearing carbonate, burbankite, occurs in thin microcrystalline coatings and veinlets with mckelveyite-ewaldite at the base of the Wilkins Peak member of the Green River Formation in Sweetwater County, Wyoming. Fragments yield excellent powder patterns from which the hexagonal cell dimensions have been determined to be a 10.451(3), c 6.510(2) Å, very close to those of burbankite from Mont St. Hilaire, Quebec. The Wyoming burbankite is heavily contaminated with organic matter which can be removed by moderate heating. The decomposition temperature in air of this burbankite is near 600°C; the products of decomposition have been partly identified. The morphology has been examined by scanning electron microscopy, which shows that the prismatic habit of even the smallest crystallites is similar to the habit of megascopic burbankite from some other localities. Microprobe analysis shows that the Wyoming burbankite is extremely rare-earth rich and approaches the upper limit of rare-earth content imposed by stoichiomery. Calculated sigma values for burbankites from several localities show a fairly restricted range of variation at high atomic percentages of Ce, La, and Pr.

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