Anningite-(Ce), (Ca _0.5 Ce ⁴⁺ _0.5 )(VO ₄ ), a new mineral from phosphate coprolite of the Gara Samani Formation, Algeria

Abstract Anningite-(Ce) ideally (Ca 0.5 Ce 4+ 0.5 )(VO 4 ), was found within a phosphate coprolite from the sand-dominated sediments of the Gara Samani Formation, Algeria. As a tetragonal anhydrous vanadate, this mineral is classified in the xenotime group. It occurs in rock cavities and forms small (typically up to 100 μm in length) sheaf-like aggregates composed of crystals 30–40 μm in length and ∼7 μm in diameter. Anningite-(Ce) crystals are green with a vitreous lustre. No cleavage is observed and the fracture is uneven or conchoidal. Its empirical formula, calculated on the basis of 4 oxygen atoms, can be written as (Ca 0.52 Ce 4+ 0.47 Y 3+ 0.01 ) Σ1.00 [(VO 4 ) 0.88 (PO 4 ) 0.05 (SO 4 ) 0.06 (SiO 4 ) 0.01 ] Σ1.00 . The calculated density is 3.887 g/cm 3 . Anningite-(Ce) is tetragonal with space group I 4 1 / amd and unit-cell parameters a = 7.1500(4) Å, c = 6.3343(7) Å, and V = 323.82(5) Å 3 . Anningite-(Ce) is isostructural with wakefieldite-(Ce).