Crystal chemistry of schreibersite, (Fe,Ni)3P

Abstract

Schreibersite, (Fe,Ni)3P, the most abundant cosmic phosphide, is a principal carrier of phosphorus in the natural Fe-Ni-P system and a likely precursor for prebiotic organophosphorus compounds at the early stages of Earth’s evolution. The crystal structure of the mineral contains three metal sites allowing for unrestricted substitution of Fe for Ni. The distribution of these elements across the structure could serve as a tracer of crystallization conditions of schreibersite and its parent celestial bodies. However, discrimination between Fe (Z = 26) and Ni (Z = 28) based on the conventional X-ray structural analysis was for a long time hampered due to the proximity of their atomic scattering factors. We herein show that this problem has been overcome with the implementation of area detectors in the practice of X-ray diffraction. We report on previously unknown site-specific substitution trends in schreibersite structure. The composition of the studied mineral encompasses a Ni content ranging between 0.03 and 1.54 Ni atoms per formula unit (apfu): the entire Fe-dominant side of the join Fe3P-Ni3P. Of 23 schreibersite crystals studied, 22 comprise magmatic and non-magmatic iron meteorites and main group pallasites. The near end-member mineral (0.03 Ni apfu) comes from the pyrometamorphic rocks of the Hatrurim Basin, Negev desert, Israel. It was found that Fe/Ni substitution in schreibersite follows the same trends in all studied meteorites. The dependencies are nonlinear and can be described by second-order polynomials. However, the substitution over the M2 and M3 sites within the most common range of compositions (0.6 < Ni <1.5 apfu) is well approximated by a linear regression: Ni(M2) = 0.84 × Ni(M3) – 0.30 apfu (standard error 0.04 Ni apfu). The analysis of the obtained results shows a strong divergence between the variation of unit-cell parameters of natural schreibersite and those of synthetic (Fe,Ni)3P. This indicates that Fe/Ni substitution trends in the mineral and its synthetic surrogates are different. A plausible explanation might be related to the differences in the system equilibration time of meteoritic schreibersite (millions of years) and synthetic (Fe,Ni)3P (~100 days). However, regardless of the reason for the observed difference, synthetic (Fe,Ni)3P cannot be considered a structural analog of natural schreibersite, and this has to be taken into account when using synthetic (Fe,Ni)3P as an imitator of schreibersite in reconstructions of natural processes.

Nazarovite, Ni12P5, a new terrestrial and meteoritic mineral structurally related to nickelphosphide, Ni3P

“…The nazarovite framework (Fig. 3a,b) is topologically similar to that of the minerals belonging to schreibersite-nickelphosphide join, Fe 3 P-Ni 3 P (Britvin et al 2021a). Both nazarovite and nickelphosphide are tetragonal, have very similar lattice metrics (Table 3), and the relationship between their unit-cell contents can be expressed as 2×Ni 12 P 5 (Ni 24 P 10 ) ↔ 8×Ni 3 P (Ni 24 P 8 ).…”

“…The influence of crystal-chemical factors on the processes of elemental differentiation in reduced systems is a largely obscure field of mineralogy and geochemistry. Here the most prominent is the Fe-Ni system (e.g., Goldstein et al 2009) Britvin et al 1999Britvin et al , 2021a[3] Ilnitskaya et al 1987;[4] Oryshchyn et al 2004;[5]…”

“…The crystal-chemical misfits result in unexpectedly restricted Fe/Ni substitutions. In fact, the joins Fe 3 P-Ni 3 P (schreibersitenickelphosphide) and Fe 2 P-Ni 2 P (barringerite-transjordanite) are the only examples of continuous Fe-Ni solid solutions (Britvin et al 2020a(Britvin et al , 2021a. A limited Fe-Ni miscibility was reported in murashkoite (Vereshchagin et al 2021), zuktamrurite, allabogdanite (Britvin et al 2019b) and melliniite, whereas other phosphides do not show traceable Fe/Ni substitutions.…”

Kaznakhtite, Ni6Co3+2(CO3)(OH)16⋅4H2O, a new natural layered double hydroxide, the member of the hydrotalcite supergroup

“…We used 20-order Chebyshev polynomial to describe a complex shape of background curve (Fig. 7), because this fit was successfully employed in previous crystallographic works dealing with Rigaku RAXIS image-plate data (e.g., Britvin et al, 2021). Octahedral cation site occupancy was constrained according to the data of electron microprobe analysis.…”

Discovery of terrestrial andreyivanovite, FeCrP, and the effect of Cr and V substitution on the low-pressure barringerite-allabogdanite transition

“…The Hatrurim Complex has recently become known as a source of terrestrial phosphides (Britvin et al 2015). Here, besides the phosphides typical of meteorites: schreibersite, Fe 3 P (Britvin et al 2021a), barringerite, Fe 2 P (Britvin et al 2017) and its high-pressure analogallobogdanite (Britvin et al 2021b), nine new phosphides: halamishite, Ni 5 P 4 (Britvin et al 2020a); negevite, NiP 2 (Britvin et al 2020b); nazarovite, Ni 12 P 5 (Britvin et al 2022a); zuktamrurite, FeP 2 (Britvin et al 2019a); transjoardanite, Ni 2 P (Britvin et al 2020c); polekhovskyite, MoNiP 2 (Britvin et al 2022b); murashkoite, FeP (Britvin et al 2019b); nickolayite, FeMoP (Murashko et al 2019); orishchinite, Ni 2 P (Britvin et al 2019c) were discovered. This detection of phosphides in the rocks of the Hatrurim Complex is unexpected.…”