Kesebolite-(Ce), CeCa2Mn(AsO4)[SiO3]3, a new REE-bearing arsenosilicate mineral from the Kesebol mine, Åmål, Västra Götaland, 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 V&auml
stra G&ouml
taland, 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 ncalc = 1.74. H = 5&ndash
6 and VHN100 = 825. Fair cleavage is observed on {100}. The calculated density is 3.998(5) g&middot
cm&minus
3. Kesebolite-(Ce) is monoclinic, P21/c, with unit-cell parameters from X-ray single-crystal diffraction data: a = 6.7382(3), b = 13.0368(6), c = 12.0958(6) &Aring
&beta
= 98.578(2)&deg
and V = 1050.66(9) &Aring
3, with Z = 4. Strongest Bragg peaks in the X-ray powder pattern are: [I(%), d(&Aring
) (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).