Publication Date:
2022-02-28
Description:
A crystal chemical investigation of a natural specimen of whitlockite, ideally
Ca9Mg(PO4)6[PO3(OH)], from Palermo Mine (USA), was achieved by means of a combination of
electron microprobe analysis (EMPA) in WDS mode, single‐crystal neutron diffraction probe (NDP)
and single‐crystal X‐ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. The
crystal‐chemical characterization resulted in the empirical formula
(Ca8.682Na0.274Sr0.045)Σ9.000(Ca0.034□0.996)Σ1.000(Mg0.533Fe2+0.342Mn2+0.062Al0.046)Σ0.983(P1.006O4)6[PO3(OH0.968F0.032)Σ1.000].
Crystal‐structure refinement, in the space group R3c, converged to R1 = 7.12% using 3273 unique
reflections from NDP data and to R1 = 2.43% using 2687 unique reflections from XRD data. Unit cell
parameters from NDP are a = 10.357(3) Å, c = 37.095(15) Å and V = 3446(2) Å3, and from XRD, the
parameters are a = 10.3685(4) Å, c = 37.1444(13) Å and V = 3458.2(3) Å3. NDP results allowed a deeper
definition of the hydrogen‐bond system and its relation with the structural unit [PO3(OH)]. The
FTIR spectrum is very similar to that of synthetic tricalcium phosphate Ca3(PO4)2 and displays
minor band shifts due to slightly different P‐O bond lengths and to the presence of additional
elements in the structure. A comparison between whitlockite, isotypic phases from the largest
merrillite group, and its synthetic counterpart Ca3(PO4)2 is provided, based on the XRD/NDP and
FTIR results.
Description:
Published
Description:
225
Description:
1TR. Georisorse
Description:
JCR Journal
Keywords:
whitlockite
;
calcium phosphates
;
Mineralogy
;
crystal chemistry
;
spectroscopy
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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