Abenakiite-(Ce)

Abenakiite-(Ce) is a mineral of sodium, cerium, neodymium, lanthanum, praseodymium, thorium, samarium, oxygen, sulfur, carbon, phosphorus, and silicon with a chemical formula Na26Ce6(SiO3)6(PO4)6(CO3)6(S4+O2)O. The silicate groups may be given as the cyclic Si6O18 grouping. The mineral is named after the Abenaki, an Algonquian Indian tribe of New England. Its Mohs scale rating is 4 to 5.

Occurrence and association
Abenakiite-(Ce) was discovered in a sodalite syenite xenolith at Mont Saint-Hilaire, Québec, Canada, together with aegirine, eudialyte, manganoneptunite, polylithionite, serandite, and steenstrupine-(Ce).

Notes on chemistry and relation to other species
Combination of elements in abenakiite-(Ce) is unique. Somewhat chemically similar mineral is steenstrupine-(Ce). The hyper-sodium abenakiite-(Ce) is also unique in supposed presence of sulfur dioxide ligand. With a single grain (originally) found, abenakiite-(Ce) is extremely rare.

Crystal structure
In the crystal structure, described as a hexagonal net, of abenakiite-(Ce) there are:
 * chains of NaO7 polyhedra, connected with PO4 groups
 * columns with six-membered rings of NaO7, and NaO7-REEO6, and SiO4 polyhedra (REE – rare earth elements)
 * CO3 groups, NaO6 octahedra, and disordered SO2 ligands within the columns