Akermanite (Ca₂MgSi₂O₇, S5₃)

Unit cell

Lattice constants

a = 7.834 Å, b = 7.834 Å, c = 5.008 Å; α = 90.00°, β = 90.00°, γ = 90.00°

Cell volume

307.3 ų

Atoms in the conventional cell

24 (Mg 2, O 14, Ca 4, Si 4)

Formula units Z

2

Pearson symbol

tP24 — tetragonal, primitive lattice, 24 atoms per conventional cell

Symmetry operations

8 per cell

Crystallographic sites

The multiplicity and the Wyckoff letter say how many copies of the site the group makes in one cell and on which kind of symmetry element the site sits; the 24 atoms drawn above are these sites multiplied by all 8 operations. Press Wyckoff under Colour to see the sites, and tick a symmetry element on the left to see which atoms lie on it.

How to read the label

A2BC7D2_tP24_113_e_a_cef_e-001: the stoichiometry comes first (A, B, C… are the elements in alphabetical order of their site labels), then the Pearson symbol tP24, then the space-group number 113, then the Wyckoff letters occupied by each element in turn (Mg: 2a; O: 2c; Ca: 4e; O: 4e; Si: 4e; O: 8f). Two structures with the same label are the same arrangement with different cell parameters or coordinates.

Other compounds with this structure

Ba₂CdSi₂O₇, Ba₂CoGe₂O₇, Ba₂CoSi₂O₇, Ba₂CuGe₂O₇, Ba₂CuSi₂O₇, Ba₂FeGe₂O₇, Ba₂MgGe₂O₇, Ba₂MgSi₂O₇, Ba₂MnGe₂O₇, Ba₂MnSi₂O₇, Ba₂ZnGe₂O₇, Ca₂BeSi₂O₇ (gugiaite), Ca₂CoSi₂O₇, Ca₂GeGa₂O₇, Ca₂MgSi₂O₇, Ca₂SiAl₂O₇ (gehlenite), Ca₂SiB₂O₇ (okayamalite), Ca₂SiGa₂O₇, Ca₂ZnGe₂O₇, Ca₂ZnSi₂O₇ (hardystonite), Dy₂GeBe₂O₇, Er₂GeBe₂O₇, Eu₂GeGa₂S₇, Eu₂MgSi₂O₇, Eu₂MnSi₂O₇, Gd₂GeBe₂O₇, Ho₂GeBe₂O₇, Ho₂SiBe₂O₇, K₂CoV₂O₇, K₂CuP₂O₇, K₂FeP₂O₇, K₂MnV₂O₇, La₂GeBe₂O₇, Na₂LiBe₂F₇, Na₂ZnV₂O₇, Nd₂GeBe₂O₇, Pr₂GeBe₂O₇, Sm₂GeBe₂O₇, Sr₂CoGe₂O₇, Sr₂CoSi₂O₇, Sr₂CuGe₂O₇, Sr₂CuSi₂O₇, Sr₂GeFe₂O₇, Sr₂MgGe₂O₇, Sr₂MgSi₂O₇, Sr₂MnGe₂O₇, Sr₂MnS

Note: S5₃ Akermanite.

Source

Coordinates and cell from the AFLOW Encyclopedia of Crystallographic Prototypes, entry A2BC7D2_tP24_113_e_a_cef_e-001 (M. J. Mehl et al., Comput. Mater. Sci. 136, S1 (2017); D. Hicks et al., ibid. 161, S1 (2019) and 199, 110450 (2021); S. Eckert et al., ibid. 240, 112988 (2024)). Symmetry elements, Wyckoff assignment and the diagram are computed on this page from the group operations.