Keplerite is a new mineral, the Ca-dominant counterpart of the most abundant meteoritic phosphate, merrillite. The isomorphous series merrillite-keplerite, Ca 9 NaMg(PO 4 ) 7 -Ca 9 (Ca 0.5 □ 0.5 )Mg(PO ) 7 represents the main reservoir of phosphate phosphorus in the Solar System. Both minerals are related by the heterovalent substitution at the B-site of the crystal structure: 2Na + (merrillite) → Ca 2+ + □ (keplerite). The near-end-member keplerite of meteoritic origin occurs in the main-group pallasites and angrites. The detailed description of the mineral is made based on the Na-free type material from the Marjalahti meteorite (the main group pallasite). Terrestrial keplerite was discovered in the pyrometamorphic rocks of the Hatrurim Basin in the northern part of Negev desert, Israel. Keplerite grains in Marjalahti have an ovoidal to cloudy shape and reach 50 μm in size. The mineral is colorless, transparent with a vitreous luster. Cleavage was not observed. In transmitted light, keplerite is colorless and non-pleochroic. Uniaxial (−), ω 1.622(1), ε 1.619(1). Chemical composition (electron microprobe, wt.%): CaO 48.84; MgO 3.90; FeO 1.33; P 2 O 5 46.34, total 100.34. The empirical formula (O = 28 apfu) is: Ca 9.00 (Ca 0.33 Fe 2+ 0.20 □ 0.47 ) 1.00 Mg 1.04 P 6.97 O 28 .The ideal formula is Ca 9 (Ca 0.5 □ 0.5 )Mg(PO 4 ) 7 . Keplerite is trigonal, space group R3c, unit-cell parameters refined from single-crystal data are: a 10.3330(4), c 37.0668(24) Å, V 3427.4(3) Å 3 , Z = 6. The calculated density is 3.122 g cm -3 . The crystal structure has been solved and refined to R 1 = 0.039 based on 1577 unique observed reflections [I >2σ(I)]. A characteristic structural feature of keplerite is a partial (half-vacant) occupancy of the sixfold-coordinated B-site (denoted as CaIIA in the earlier works). The disorder caused by this cation vacancy is the most likely reason for the visually resolved splitting of the ν 1 (symmetric stretching) (PO 4 ) vibration mode in the Raman spectrum of keplerite. The mineral is an indicator of high-temperature environments characterized by extreme depletion of Na. The association of keplerite with "REE-merrillite" and stanfieldite evidences for the similarity of temperature conditions occurred in the Mottled Zone to those This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

Xenophyllite, ideally Na4Fe7(PO4)6, is a rare meteoritic phosphate found in phosphide-phosphate assemblages confined to troilite nodules of the Augustinovka iron meteorite (medium octahedrite, IIIAB). The mineral occurs as tiny lamella up to 0.15 mm long cross-cutting millimeter-sized grains of sarcopside, Fe3(PO4)2, associated with schreibersite, chromite and pentlandite. Xenophyllite is translucent, has a bluish-green to grey-green color and vitreous lustre. Moh’s hardness is 3.5–4. Cleavage is perfect on {001}. Measured density is 3.58(5) g/cm3. The mineral is biaxial (−), 2V 10–20°, with refractive indexes: α 1.675(2), β 1.681(2), γ 1.681 (2). Chemical composition of the holotype specimen (electron microprobe, wt.%) is: Na2O 10.9, K2O 0.4, MnO 5.8, FeO 42.1, Cr2O3 0.8, P2O5 40.7, total 100.7, corresponding to the empirical formula (Na3.67K0.09)Σ3.76(Fe2+6.12Mn2+0.85Cr0.11)Σ7.08P5.99O24.00. Xenophyllite is triclinic, P1 or P-1, a 9.643(6), b 9.633(5), c 17.645(11) Å; α 88.26(5), β 88.16(5), γ 64.83(5)°, V 1482(2) Å3, Z = 3. The toichiome C-centered subcell has the following dimensions: a 16.257(9), b 10.318(8), c 6.257(9) Å, β = 112.77(9)°, V 968(2) Å3, Z = 2. Xenophyllite is structurally related to synthetic phosphate Kna3Fe7(PO4)6 having a channel-type structure, and galileiite, NaFe4(PO4)3. The variations of chemical composition of xenophyllite ranging from Na4Fe7(PO4)6 to almost Na2Fe8(PO4)6 are accounted for by Na-ions mobility. The latter property makes xenophyllite a promising prototype for cathode materials used in sodium-ion batteries.

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, is a new natural phosphide discovered on Earth and in meteorites. Terrestrial nazarovite originates from phosphide assemblages confined to pyrometamorphic suite of the Hatrurim Formation (the Mottled Zone), the Dead Sea basin, Negev desert, Israel. Meteoritic nazarovite was identified among Ni-rich phosphide precipitates extracted from the Marjalahti meteorite (main group pallasite). Terrestrial mineral occurs as micrometer-sized lamella intergrown with transjordanite (Ni2P). Meteoritic nazarovite forms chisel-like crystals up to 8 μm long. The mineral is tetragonal, space group I4/m. The unit-cell parameters of terrestrial and meteoritic material, respectively: a 8.640(1) and 8.6543(3), c 5.071(3), and 5.0665(2) Å, V 378.5(2), and 379.47(3) Å3, Z = 2. The crystal structure of terrestrial nazarovite was solved and refined on the basis of X-ray single-crystal data (R1 = 0.0516), whereas the structure of meteoritic mineral was refined by the Rietveld method using an X-ray powder diffraction profile (RB = 0.22%). The mineral is structurally similar to phosphides of schreibersite–nickelphosphide join, Fe3P-Ni3P. Chemical composition of nazarovite (terrestrial/meteoritic, electron microprobe, wt%): Ni 81.87/78.59, Fe <0.2/4.10; Co <0.2/0.07, P 18.16/17.91, total 100.03/100.67, leading to the empirical formula Ni11.97P5.03 and (Ni11.43Fe0.63Co0.01)12.07P4.94, based on 17 atoms per formula unit. Nazarovite formation in nature, both on Earth and in meteorites, is related to the processes of Fe/Ni fractionation in solid state, at temperatures below 1100 °C.

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