Nomenclature of the ancylite supergroup

The ancylite supergroup is approved by the IMA-CNMNC, with the general crystal chemical formula (M3+xM2+2-x)(CO3)2[(OH)x·(2–x)H2O] (1 ≤ x ≤ 2, Z = 2). The ancylite supergroup can be divided into two groups defined by different proportions of the M cation and hydroxyl anion and/or water molecule: the ancylite group is defined for 1 ≤ x ≤ 1.5; the kozoite group is defined for 1.5 < x ≤ 2. The ancylite supergroup minerals are orthorhombic with space group Pmcn, or monoclinic with space group Pm11, and have a crystal structure with species-defining trivalent and divalent M cations (M = La3+, Ce3+, Nd3+, Ca2+, Sr2+ and Pb2+) which centre ten-vertex polyhedron formed by oxygen atoms at three independent O sites. At the vertices of triangular (CO3)2- anion, two are oxygen atoms, while the third one, O(3), is statistically filled with (OH)- groups and H2O molecules. The triangular faces of three oxygen atoms of MO10 coordination polyhedra join the chains of this ten-vertex polyhedral, which is extended along the c axis. (CO3) triangles connect chains in three dimensions. Up to now, eight valid mineral species with M2+ = Sr2+, Ca2+ and Pb2+ belong to the ancylite group [ancylite-(La), ancylite-(Ce), calcioancylite-(La), calcioancylite-(Ce), calcioancylite-(Nd), gysinite-(La), gysinite-(Ce), and gysinite-(Nd)]. Two hydroxyl carbonates with only rare earth elements as species-defining cations, kozoite-(La) and kozoite-(Nd) are members of the kozoite group.