Ferriandrosite-(Ce), a new member of the epidote supergroup from Betliar, Slovakia

A new member of the epidote supergroup, ferriandrosite-(Ce), ideally MnCeFe3+AlMn2+(Si2O7)(SiO4)O(OH), was found at the Julius manganese ore occurrence near Betliar, Roznava Co., Kosice Region, Slovakia. It occurs as subhedral grains and polycrystalline aggregates, up to 0.3 mm in size, enclosed in pyroxmangite. Other associated minerals are spessartine, rhodochrosite, quartz, baryte and pyrosmalite-(Mn). Ferriandrosite-(Ce) is dark brown, with a light brown streak and vitreous lustre. The Mohs hardness is similar to 6 1/2 to 7 and tenacity is brittle with no observable cleavage or fracture. The calculated density is 4.321 g.cm(-3). Ferriandrosite-(Ce) is optically biaxial (+), with weak pleochroism, high surface relief and the mean calculated refractive index is 1.832. The empirical structural formula of ferriandrosite-(Ce), based on 13 anions per formula unit, is (A1)(Mn0.632+Ca0.35Ce0.02)Sigma(A2)(1.00)(Ce0.53La0.27Nd0.14Pr0.05REE0.01 star)(Sigma 1.00)(M1)(Fe0.413+Al0.12V0.013+Mg0.40Ti0.05)(Sigma 0.99)(M2) Al-1.00(M3)(Mn0.752+Fe0.222+Mg0.03)(Sigma 1.00)(T1-3Si3.00O11O4)(O0.67F0.33)(OH), where REE star are minor rare earth elements. Ferriandrosite-(Ce) is monoclinic, space group P2(1)/m, a = 8.8483(4) angstrom, b = 5.7307(3) angstrom c = 10.0314(5) angstrom, beta = 113.3659(15)degrees, V = 466.95(4) angstrom(3) and Z = 2. The crystal structure of ferriandrosite-(Ce) was refined to a final R-1 = 0.0210 for 1910 reflections with F-o > 4(sigma)(F-o) and 127 refined parameters. Structural features of ferriandrosite-(Ce) are discussed and compared with other members of the androsite-series.