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]. It is named after the Abenaki, an Algonquian Indian tribe of New England. Its Mohs scale rating is 4 to 5.

  • Category: Silicate, Cyclosilicate
  • Formula: (repeating unit) Na26Ce6(SiO3)6 (PO4)6 (CO3)6 (S4+ O2)O
  • Crystal system: Trigonal

Currently the only mineral with a supposed sulphur dioxide ligand. Originally a single grain was found, making the mineral exceedingly rare.

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.

Physical Properties of Abenakiite-(Ce)

  • Cleavage: {0001} Poor
  • Color: Pale brown.
  • Density: 3.21
  • Diaphaneity: Transparent
  • Fracture: Brittle – Conchoidal – Very brittle fracture producing small, conchoidal fragments.
  • Habit: Euhedral Crystals – Occurs as well-formed crystals showing good external form.
  • Hardness: 4 – Fluorite
  • Luminescence: Non-fluorescent.
  • Luster: Vitreous (Glassy)
  • Streak: white


Information Source: