- journal_title：The Canadian Mineralogist
- Contributor：Mark A. Cooper ; Frank C. Hawthorne ; Petr Černý
- Publisher：Mineralogical Association of Canada
- Date：2009-
- Format：text/html
- Language：en
- Identifier：10.3749/canmin.47.1.173
- journal_abbrev：Can Mineral
- issn：0008-4476
- volume：47
- issue：1
- firstpage：173
- section：Articles
The crystal structure of ercitite, ideally Na2(H2O)4[Mn3+2(OH)2(PO4)2], orthorhombic, a 6.2499(6), b 8.7479(9), c 19.9554(17) Å, V 1091.0 Å3, space group Cmca, Z = 4, Dcalc = 2.77 g.cm−3, from the Tanco granitic pegmatite, Bernic Lake, southeastern Manitoba, Canada, has been solved by direct methods and refined to R1 = 4.0% on the basis of 431 unique observed reflections | Fo ≥ 4σF | collected on a Bruker P4 diffractometer equipped with a CCD 1K Smart detector and MoKα radiation. There is one distinct P site occupied by P and coordinated by four O atoms in an tetrahedral arrangement, with a <P–O> distance of 1.541 Å. There are two octahedrally coordinated M sites: M(1) is occupied by (Mn3+0.53Fe3+0.46Al0.01) with a <M(1)–O> distance of 2.028 Å, and M(2) is occupied by (□0.93Mn2+0.07) with a <M(2)–O> distance of 2.252 Å. The M(1) octahedron shows four short meridional bonds (~1.95 Å) and two long apical bonds (2.176 Å) characteristic of Jahn–Teller-distorted octahedrally coordinated Mn3+. There is one distinct Na site occupied by (Na0.89Ca0.04□0.07) and coordinated by six anions with a <Na–O> distance of 2.504 Å. The structural unit in ercitite, [Mn3+2(OH)2(PO4)2], is chemically and topologically identical to the structural unit in bermanite, Mn2+(H2O)4[Mn3+2(OH)2(PO4)2]. However, the stacking of these sheet-like units differs between the two minerals; the sheets in ercitite link through corner-sharing of [7]-coordinated Na polyhedra that share edges with the polyhedra of the structural units, whereas the sheets in bermanite link by sharing polyhedron corners with interstitial {Mn2+O2(H2O)4} octahedra.