Kesebolite-(Ce), CeCa2Mn(AsO4) SiO3 (3), a New REE-Bearing Arsenosilicate Mineral from the Kesebol Mine, angstrom mal, Vastra Gotaland, Sweden

Kesebolite-(Ce), ideal formula CeCa2Mn(AsO4)[SiO3](3), is a new mineral (IMA No. 2019-097) recovered from mine dumps at the Kesebol Mn-(Fe-Cu) deposit in Vastra Gotaland, Sweden. It occurs with rhodonite, baryte, quartz, calcite, talc, andradite, rhodochrosite, K-feldspar, hematite, gasparite-(Ce), chernovite-(Y) and ferriakasakaite-(Ce). It forms mostly euhedral crystals, with lengthwise striation. The mineral is dark grayish-brown to brown, translucent, with light brown streak. It is optically biaxial (+), with weak pleochroism, and n(calc) = 1.74. H = 5-6 and VHN100 = 825. Fair cleavage is observed on {100}. The calculated density is 3.998(5) gcm(-3). Kesebolite-(Ce) is monoclinic, P2(1)/c, with unit-cell parameters from X-ray single-crystal diffraction data: a = 6.7382(3), b = 13.0368(6), c = 12.0958(6) angstrom, beta = 98.578(2)degrees, and V = 1050.66(9) angstrom(3), with Z = 4. Strongest Bragg peaks in the X-ray powder pattern are: [I(%), d(angstrom) (hkl)] 100, 3.114 (20-2); 92, 2.924 (140); 84, 3.138 (041); 72, 2.908 (014); 57, 3.228 (210); 48, 2.856 (042); 48, 3.002 (132). The unique crystal structure was solved and refined to R1 = 4.6%. It consists of 6-periodic single silicate chains along (001); these are interconnected to infinite (010) strings of alternating, corner-sharing MnO6 and AsO4 polyhedra, altogether forming a trellis-like framework parallel to (100).