Abstract Esdanaite- (Ce), ideally NaMnCe (PO4) 2·4H2O, is a new mineral discovered at the Poudrette Quarry, Mont Saint-Hilaire, Québec, Canada. It occurs in segregations within sodalitites, where it develops in radiating, spiky spherical aggregates composed of bladed crystals, these having average dimensions of 40 × 5 μm. Individual crystals are 1 μm thick, dominated by the pinacoid 001, and are white or pale pink in color. Associated minerals include albite, sodalite, aegirine, natrolite, a lovozerite-group mineral, rhodochrosite, sphalerite, a eudialyte-group mineral, and petersenite- (Ce). Esdanaite- (Ce) has a vitreous luster, is translucent, and has a white streak. It is brittle and has a hackly fracture. No cleavage was observed, but it is hypothesized to possess a moderate 001 cleavage based on crystal-structure considerations. No fluorescence was observed under short-, medium-, or long-wave radiation. The calculated density is 3. 14 g/cm3. Separation of a crystal suitable for optics was unsuccessful; an average refractive index of n = 1. 311 was calculated. The mineral is presumed biaxial based on orthorhombic symmetry. An average of 22 analyses gave (range, standard deviation) of (wt. %) Na2O 3. 65 (2. 80–4. 74, 0. 55), P2O5 31. 65 (28. 32–33. 57, 1. 23), CaO 2. 40 (2. 15–3. 03, 0. 17), MnO 15. 57 (14. 46–16. 10, 0. 41), SrO 2. 55 (2. 20–2. 94, 0. 21), La2O3 8. 54 (8. 03–9. 01, 0. 25), Ce2O3 14. 12 (13. 03–14. 90, 0. 46), Pr2O3 4. 59 (4. 19–4. 98, 0. 19), Nd2O3 3. 91 (3. 54–4. 31, 0. 15), Sm2O3 0. 55 (0. 39–0. 76, 0. 11), and H2O (calc. ) 15. 76, total 103. 28 wt. %. The empirical formula (based on 12 anions) is (Na0. 54□0. 26Ca0. 20) Σ1. 00Mn1. 00 (Ce0. 39La0. 24Pr0. 13Sr0. 11Nd0. 11Sm0. 01) Σ0. 99P2. 04O8·4H2O. Esdanaite- (Ce) is orthorhombic, crystallizing in space group P212121 (No. 19), with a = 6. 4690 (13), b = 7. 1790 (14), and c = 21. 456 (4) Å, V = 996. 4 (3) Å3, Z = 1. The strongest six lines of the X-ray powder diffraction pattern d in Å (I) (hkl) are 10. 717 (100) (002), 2. 761 (20) (025), 2. 921 (20) (211), 3. 581 (18) (006), 2. 725 (16) (213), 3. 209 (12) (023). A Raman spectrum, which has strong lines 461 and 951 cm−1 (corresponding to P–O bending and P–O stretching), strongly resembles that of more simple phosphate minerals. The crystal structure was determined by single-crystal X-ray methods and refined to R = 3. 85%, wR2 = 5. 31%. It is characterized by infinite sheets of polymerized PO4 tetrahedra and Mnϕ6 (ϕ = O or H2O) octahedra that form on 001. The sheets are corrugated, leading to the development of continuous “troughs” along 100 and channels along 010, each being occupied by Naϕ7 and Ceϕ9 polyhedra, respectively. Gaps between adjacent PO4–Mnϕ6 layers are occupied by H2O groups. This crystal structure is unique among known phosphate minerals and does not appear to have a synthetic equivalent. Esdanaite- (Ce) is a paragenetically late-stage mineral that formed as a result of late-stage alkaline fluids enriched in P interacting with precursor minerals in the sodalitite (possibly a eudialyte-group mineral) under conditions of low P and T.
Gore et al. (Fri,) studied this question.