Unusual variety of forsterite strongly enriched by pentavalent constituents, phosphorus and arsenic (up to 12.9 wt% P2O5 and up to 16.0 wt% As2O5) was found in sublimates of the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia, in association with As- and P-depleted forsterite, anhydrite, diopside, hematite, spinel, haüyne, fluorapatite, svabite, berzeliite, calciojohillerite, and arsenudinaite. This forsterite is the P-richest natural olivine which also demonstrates first case of As incorporation in an olivine-type silicate. P- and As-rich forsterite is orthorhombic, space group Pbnm, unit-cell parameters are: a = 4.7762(2), b =10.2643(4), c = 5.9646(2) Å and V = 292.41(2) Å3. Its crystal structure was solved on single crystal and refined to R = 2.88%. The crystal chemical formula is M(1)(Mg0.83[vac]0.17)M(2)(Mg0.95[vac]0.05)[Si0.56P0.32As0.12]O4. The substitution scheme for the incorporation of pentavalent constituents in forsterite is: VIMg2+ + 2IVSi4+ ↔ VI[vac]0 + 2IVT5+, in which T5+ = P, As and [vac] = vacancy. No sign of vacancies in the tetrahedrally coordinated T site is found.

中文翻译：

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富含砷和磷的天然镁橄榄石：化学、晶体结构、晶体形态和分带

在 Arsenatnaya 喷气孔、Tolbachik 火山、俄罗斯堪察加半岛的升华物中发现了富含五价成分、磷和砷（高达 12.9 wt% P2O5 和高达 16.0 wt% As2O5）的不同寻常的镁橄榄石，与 As- 和贫磷镁橄榄石、硬石膏、透辉石、赤铁矿、尖晶石、haüyne、氟磷灰石、svabite、berzeliite、calciojohillerite和arsenudinaite。这种镁橄榄石是磷含量最高的天然橄榄石，它也展示了第一个在橄榄石型硅酸盐中掺入砷的案例。富含 P 和 As 的镁橄榄石是斜方晶系，空间群 Pbnm，晶胞参数为：a = 4.7762(2), b =10.2643(4), c = 5.9646(2) Å 和 V = 292.41(2) Å3。其晶体结构在单晶上解析并精制至 R = 2.88%。晶体化学式为 M(1)(Mg0.83[vac]0.17)M(2)(Mg0.95[vac]0.05)[Si0.56P0。32As0.12]O4。在镁橄榄石中引入五价成分的取代方案是：VIMg2+ + 2IVSi4+ ↔ VI[vac]0 + 2IVT5+，其中 T5+ = P，As 和 [vac] = 空位。在四面体配位的 T 位点中没有发现空位的迹象。