Annotation of the results obtained in 2020
The most significant result of this project (both of the current year and as a whole) was the discovery of natural cyclophosphates – the likely precursors of prebiotic organophosphorus compounds that gave rise to the emergence of primitive life on our planet. Unlike orthophosphates common in nature and chain polyphosphates (known as single findings), the structures of cyclophosphates contain (PO4) tetrahedra condensed into the cycle. Thus, the cyclophosphates we discovered in the course of current project have the maximum degree of condensation of (PO4) tetrahedra among natural phosphates. The cyclic structure leads to a considerable steric strain within the phosphate ring. Because of that, cyclophosphates are regarded as energy-rich compounds. It was shown that the hydrolytic breakdown (ring opening) of phosphate cycle liberates the chemical energy up to 40 kJ mol-1 that is sufficient for the onset of catalysts-free phosphorylation - phosphoester P–O–C bond formation. Due to that, cyclophosphates are considered as potential compounds involved in the formation of primary biomolecules on the early Earth. Unfortunately, all hypotheses relied upon cyclophosphate-based phosphorylation have met an unavoidable obstacle. Until now, cyclophosphates have neither been encountered in nature. We have discovered these minerals in the pyrometamorphic rocks of the Hatrurim Formation (Israel). Cyclophosphates are the oxidation products of phosphides -zuctamrurite FeP2 and negevite NiP2 which were previously studied in the framework of this project. The proposed oxidation scheme of a phosphide to a cyclophosphate is quite simple: 2(Fe,Ni)P2 + 6O2 → (Fe,Ni)2P4O12 We suggest that the associations of phosphides in the vicinity of the Dead Sea and the phosphates formed from them can serve as a model system that reproduces the mineral speciation of prebiotic phosphorus on the early Earth. Taking into account the practical absence of oxygen in the Earth's atmosphere in Archean, it can be assumed that phosphides could also be oxidized by carbon dioxide: 2(Fe,Ni)P2 + 12CO2 → (Fe,Ni)2P4O12 + 12CO Therefore, the prebiotic organophosphorus compounds - precursors of primitive life on Earth could appear as a result of phosphide oxidation reactions and subsequent phosphorylation. The research results were published in the Geology journal and announced at the websites of Russian Science Foundation and Saint Petersburg State University. The next substantial result of the project was the identification of new trends in isomorphous substitutions in the minerals related to the schreibersite - nickelphosphide series, Fe3P - Ni3P. These phosphides are the main reservoir of reduced phosphorus in the solar system. The poor knowledge of these minerals is yet inconsistent with the role they play in the evolution of planetary matter. The data obtained in the course of the project have revealed very complex dependencies in Fe for Ni substitution in natural schreibersite. Moreover, we have shown that the Fe/Ni substitution in the mineral and synthetic (Fe,Ni)3P follows the diferent. The most probable reason for this discrepancy is the different equilibration time of the system during crystallization of phosphides: millions of years for meteoritic schreibersite and up to 100 days for the synthesis of (Fe,Ni)3P. Therefore, synthetic (Fe,Ni)3P cannot be considered as a structural analogue of natural schreibersite. This should be taken into account in model experiments in which synthetic (Fe,Ni)3P is used as a simulator of natural schreibersite. The research results were published in a summary article in the American Mineralogist. Keplerite, a new meteoritic phosphate discovered and studied within the framework of the project, is a Ca-analog of merrillite, Ca9MgNa(PO4)7 , and forms a continuous isomorphic series with the latter. Keplerite is named after the prominent German naturalist Johannes Kepler (1571–1630). The minerals related to the merrillite-keplerite series are the most abundant phosphates and important sodium carriers in meteoritic matter. They are considered as primary phosphorus compounds, which crystallize during the condensation of a protoplanetary nebula immediately after schreibersite. We have explored the crystal chemistry of these important phosphates, their role in sodium accumulation and their relationship with other phosphates and phosphides. Stanfieldite, a poorly studied phosphate of Ca and Mg previously known only in meteorites, was discovered for the first time on Earth during the study of terrestrial keplerite from the Hatrurim Formation. The obvious genetic relationship between keplerite, stanfieldite, and phosphides has required the in-depth study of the mineralogy and crystal chemistry of stanfieldite, which is discussed in an article published in Crystals. A detailed analysis of the crystal structure and chemical composition of the new mineral xenophyllite from phosphide-troilite-phosphate associations of the Avgustinovka meteorite was carried out. The mineral is interesting from the crystal chemical point of view, since it is a natural analogue of synthetic Na4Fe7(PO4)6, a substance that has promising applications as a material for cathodes of Na-ion batteries. The Na mobility in xenophyllite structure determines its variable chemical composition, which can vary up to a formula of Na2Fe8(PO4)6. Xenophyllite is the first mineral which adopts the alpha-CrPO4 structure type. In terms of chemical composition, xenophyllite is very close to galileiite, Na2Fe8(PO4)6, which is probably a Na-depleted chemical homologue of xenophyllite. The results of the work were published in Minerals. The data sets accumulated during the project have led to a development of promising methods for the study of transition metal phosphides. Raman spectroscopy (RS), is known as a powerful tool for the study of the structure and composition of compounds. The spatial resolution of RS is comparable to the resolution of the electron microprobe, but, contrary to the latter, RS is very tolerant to the surface quality. We have showed that this method can be successfully applied to determine the chemical composition of solid solutions of transition metal phosphides that is especially useful for the samples with irregular surface relief. The use of RS in the study of phosphides is of practical interest for materials science: powdered phosphides of Fe, Ni, and Co are among the most promising catalysts used for the splitting of water into hydrogen and oxygen - the reaction that determines the development of environmentally friendly energy. The results are published in the Journal of Alloys and Compounds. The studies planned for the project in 2020 have been completed in full. The most important results were published, according to the working plan, in 6 journal articles indexed in the Web of Science and Scopus databases, of which 4 articles are in the journals included in the first quartile (Q1). Links to the announcements: https://www.rscf.ru/news/release/na-beregakh-mertvogo-morya-nashli-veshchestva-iz-kotorykh-mogla-vozniknut-zhizn-na-zemle/ https://spbu.ru/news-events/novosti/na-beregah-mertvogo-morya-nashli-veshchestva-iz-kotoryh-mogla-vozniknut-zhizn-na https://nauka.tass.ru/nauka/10197221 https://russian.rt.com/science/article/810958-ciklofosfaty-zhizn-zemlya https://www.gazeta.ru/science/news/2020/12/08/n_15333889.shtml

 

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Annotation of the results obtained in 2018
The 2018 year of the current project involved studies related to a series of terrestrial and meteoritic phosphide minerals – sensitive evolution indicators within the cosmochemically significant Fe-Ni-P system. The study was subdivided into the two main routes. At first, we focused on the gathering new data on crystal chemistry and mineral assemblages of terrestrial Fe-Ni phosphides from pyrometamorphic rocks of the Hatrurim Formation (the Dead Sea Transform zone). A special attention has been paid to murashkoite, (Fe,Ni)P, and zuktamrurite, (Fe,Ni)P2, including detailed study of their chemical composition. The Fe for Ni substitution in the FeP – NiP and FeP2 – NiP2 solid solutions was studied for the first time, along with the previously unreported data on the FeP2 – FePS system. The crystal-chemical criteria were formulated aiming at explanation of miscibility gaps in the studied solid solutions. The second route was devoted to a study of crystal chemistry and mineral assemblages of meteoritic phosphides related to schreibersite-nickelphosphide series, Fe3P – Ni3P. The area of interest covered the meteorites related to pallasites, nickel-rich ataxites, mesosiderites, acapulcoites, enstatite chondrites and achondrites. The most valuable results were obtained while studying the meteorites related to nickel-rich ataxites. It was shown that all three studied Ni-rich ataxites (Onello, Barbianello and Santa Catharina) contain allabogdanite, (Fe,Ni)2P, closely associated with the minerals related to schreibersite-nickelphosphide series. Allabogdanite, the high-pressure analogue of barringerite, is the only known natural high-pressure phase in the Fe-Ni-P system. The occurrence of allabogdanite in the studied phosphide assemblages suggests that their host meteoritic bodies have experienced shock pressures beyond 8 GPa (80 kbar) at the temperature exceeding 1100 °C, followed by rapid quenching upon pressure release. In this sense, nickel-rich ataxites can be considered as metal-rich counterparts of a well known stony meteorites subgroup – shock-metamorphed (veined) ordinary chondrites. The results obtained in 2018 have been published or accepted for publication in 3 papers in the leading international journals, including the Q1-rank journal.

 

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Annotation of the results obtained in 2019
In accordance with the work plan for the project 18-17-00079, the following results were obtained in 2019: 1) The crystal chemistry and mineral paragenesis of the new mineral, transjordanite, (Ni,Fe)2P, from pyrometamorphic rocks of the Hatrurim formation were studied. This mineral is a nickel-dominant member of the isomorphic series of barringerite–transjordanite, Fe2P – Ni2P, the second most important series among natural phosphides from cosmochemical view point. It is shown, for the first time, that there exists a continuous series of Fe2P – Ni2P solid solutions in nature. The unexpected discovery of transjordanite in meteorites is directly related to the topics of our work, although it could not be planned before. 2) The crystal chemistry and mineral paragenesis of the new mineral, negevite, (Ni,Fe)P2, from pyrometamorphic rocks of the Hatrurim formation were studied. The variations of its chemical composition are investigated. Despite the rarity of the mineral, its discovery and study can have important genetic consequences. It is known that the synthetic analogue of Negevite refers to effective photocatalysts in an aqueous medium, significantly reducing the activation energy of many organic synthesis reactions. In this regard, the authors suggested that the mechanisms of prebiotic phosphorylation in the Archean era, traditionally associated with phosphides of the schreibersite-nickelphosphide series, could also have a catalytic nature in the case of the presence of negevite or its analogues. 3) The crystal chemistry and mineral paragenesis of the new mineral, halamishite, Ni5P4, from pyrometamorphic rocks of the Hatrurim formation were studied. The variations of its chemical composition are investigated. The mineral has two distinctive features that make it a possible temperature marker. First, halamishite, unlike most natural nickel phosphides, has no Fe- or Co- structural analogues. That’s why pure Ni5P4 is present in nature. Secondly, the stability field of the synthetic analogue of halamishite is well defined, with an upper temperature limit of 860 °C. This suggests that the temperature of the formation of phosphide associations containing halamishite did not exceed 860 ° С - i.e. they formed in the solid phase. 4) The available analytical data on the mineral paragenesis of phosphides of the Fe-Ni-P system in the rocks of the Hatrurim formation are analyzed. The results of work in this direction were most unexpected in the context of understanding the processes that led to the formation of pyrometamorphic rocks of the Dead Sea rift region. By performing a systematic study of the composition and structure of Hatrurim phosphides, we discovered allabogdanite, a high-pressure polymorph, (Fe,Ni)2P, which can be stored under normal conditions in a metastable form. 5) In 2019, as part of the current CNMMN IMA project, three new minerals - the molybdenum phosphides from the Khatrurim formation - were approved: Nickolayite, MoFeP (IMA 2018-126), Polekhovskyite, MoNiP2 (IMA 2018-147) and Orishchinite (Ni,Fe,Mo)2P (IMA 2019-039). The presence of molybdenum in siderophilic form is very unusual in natural mineral systems. 6) The chemical composition, mineral paragenesis, and crystal chemistry of minerals of the schreibersite – nickelphosphide, Fe3P – Ni3P, series from iron meteorites of the octahedrite group were studied. It was shown that (1) data obtained by standard single crystal diffractometers with MoKα radiation can be used to refine the mixed occupation of elements with such a close scattering as Fe and Ni, and (2) the Rietveld refinement of XRD powder data obtained using the effect of abnormal scattering of CoKα radiation can be successfully applied to refine the mixed occupations of Fe and Ni. These results can be of great interest for mineralogists and who have to do with the problem of determination of mixed positions occupied by the elements with close atomic numbers. In total, according to the results of studies in 2019, two articles were published in international journals indexed in the Web of Science and Scopus databases with a rating of Q1, one article was published in a journal with a rating of Q3, and another article in a journal with a rating of Q1 is now on the final review stage and is scheduled for publication in the beginning of 2020 calendar year.

 

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