Paramarkeyite, a new calcium–uranyl–carbonate mineral from the Markey mine, San Juan County, Utah, USA

• Published in: Mineralogical magazine 2022-02, Vol.86 (1), p.27-36
• Main Authors: Kampf, Anthony R., Olds, Travis A., Plášil, Jakub, Burns, Peter C., Škoda, Radek, Marty, Joe
• Format: Article
• Language: English
• Subjects: Calcite; Crystals; Gypsum; Minerals; Morphology; Spectrum analysis
• ISSN: 0026-461X; 1471-8022
• DOI: 10.1180/mgm.2021.100

The new mineral paramarkeyite (IMA2021-024), Ca 2 (UO 2 )(CO 3 ) 3 ⋅5H 2 O, was found in the Markey mine, San Juan County, Utah, USA, where it occurs as a secondary phase on gypsum-coated asphaltum in association with andersonite, calcite, gypsum and natromarkeyite. Paramarkeyite crystals are transparent, pale green-yellow, striated tablets, up to 0.11 mm across. The mineral has white streak and vitreous lustre. It exhibits moderate bluish-white fluorescence (405 nm laser). It is very brittle with irregular, curved fracture and a Mohs hardness of 2½. It has an excellent {100} cleavage and probably two good cleavages on {010} and {001}. The measured density is 2.91(2) g cm –3 . Optically, the mineral is biaxial (–) with α = 1.550(2), β = 1.556(2), γ = 1.558(2) (white light); 2V = 60(2)°; strong r > v dispersion; orientation: Y = b ; nonpleochroic. The Raman spectrum exhibits bands consistent with UO 2 2+ , CO 3 2– and O–H. Electron microprobe analysis provided the empirical formula (Ca 1.83 Na 0.20 Sr 0.03 ) Σ2.05 (UO 2 )(CO 3 ) 3 ⋅5H 2 O (+0.07 H). Paramarkeyite is monoclinic, P 2 1 / n , a = 17.9507(7), b = 18.1030(8), c = 18.3688(13) Å, β = 108.029(8)°, V = 5676.1(6) Å 3 and Z = 16. The structure of paramarkeyite ( R 1 = 0.0647 for 6657 I > 2σ I ) contains uranyl tricarbonate clusters that are linked by Ca–O polyhedra to form heteropolyhedral layers. The structure of paramarkeyite is very similar to those of markeyite, natromarkeyite and pseudomarkeyite.