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Category Silicate, Cyclosilicate
(repeating unit)
Strunz classification 9.CK.10
Crystal system Trigonal
Crystal class Rhombohedral (3)
H-M symbol: (3)
Space group R3
Unit cell a = 16.02, c = 19.76 [Å] (approximated); Z = 3
Color Pale brown
Cleavage {0001}, poor
Fracture Conchoidal
Mohs scale hardness 4-5
Luster Vitreous
Streak White
Density 3.21 (meas.), 3.27 (calc.) (approximated)
Optical properties Uniaxial (-)
Refractive index nω=1.59, nε=1.57 (approximated)
References [1][2]

Abenakiite-(Ce) (IMA1991-054) 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.[1]

Occurrence and association[edit]

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).[1][2]

Notes on chemistry and relation to other species[edit]

Combination of elements in abenakiite-(Ce) is unique. Somewhat chemically similar mineral is steenstrupine-(Ce).[2][3] 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.[1]

Crystal structure[edit]

In the crystal structure, described as a hexagonal net, of abenakiite-(Ce) there are:[1]

  • 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


  1. ^ a b c d e McDonald, A.M., Chao, G.Y., and Grice, J.D., 1994. Abenakiite-(Ce), a new silicophosphate carbonate mineral from Mont Saint-Hilaire, Quebec: Description and structure determination. The Canadian Mineralogist 32, 843-854
  2. ^ a b c Mindat, Abenakiite-(Ce), Mindat.org
  3. ^ "[International Mineralogical Association] : List of Minerals - IMA". Ima-mineralogy.org. Retrieved 2016-03-12. 

External links[edit]