Alluaivite

Alluaivite is a rare sodium calcium titanium cyclosilicate of the eudialyte group, remarkable as the only member of that group in which titanium replaces zirconium as the essential high-field-strength cation.阿卢瓦石是异性石族中稀有的钠钙钛环状硅酸盐，其特别之处在于它是该族唯一以钛而非锆作为主要高场强阳离子的成员。

It occurs in ultra-agpaitic, extremely alkaline pegmatites on Mount Alluaiv in the Lovozero massif of the Kola Peninsula, Russia, and is named for that mountain.它产于俄罗斯科拉半岛洛沃泽罗岩体阿卢瓦伊夫山的超碱性伟晶岩中，并因此山得名。

Individual accumulations do not exceed about 1 mm, and the mineral is most easily recognised by its vivid orange-red fluorescence under ultraviolet light.单个集合体不超过约 1 mm，在紫外光下呈明亮橙红色荧光，是该矿物最易识别的特征。

Discovery and naming

• Alluaivite was discovered in ultra-agpaitic pegmatite on Mount Alluaiv, in the Lovozero massif of the Kola Peninsula, Russia, and was approved as a new species in 1988.阿卢瓦石发现于俄罗斯科拉半岛洛沃泽罗岩体阿卢瓦伊夫山的超碱性伟晶岩中，并于 1988 年获批为新矿物种。
• The description was published in 1990 by Alexander P. Khomyakov, G. N. Netschelyustov and Ramiza K. Rastsvetaeva in the Proceedings of the All-Union Mineralogical Society.其描述由霍米亚科夫、涅切柳斯托夫与拉斯特斯韦塔耶娃于 1990 年发表于全苏矿物学会会刊。
• The name is taken directly from the mountain of the type locality rather than from a person or a chemical attribute.名称直接取自模式产地的山名，而非人名或化学特征。
• Type material is held in three institutions: the Mining Museum of the St. Petersburg Mining Institute under number 1993/1-2, the A. E. Fersman Mineralogical Museum in Moscow, and the Natural History Museum in London.模式标本分藏三家机构，即圣彼得堡矿业学院矿业博物馆编号 1993/1-2、莫斯科费尔斯曼矿物学博物馆，以及伦敦自然史博物馆。
• An abstract of the description appeared in American Mineralogist in 1991, which brought the species to a wider readership.该描述的摘要于 1991 年刊于《美国矿物学家》，使该矿物种为更广泛的读者所知。

Occurrence and paragenesis

• Alluaivite is confined to ultra-agpaitic pegmatites that crystallised in a strongly differentiated alkalic massif.阿卢瓦石仅产于高度分异碱性岩体中结晶的超碱性伟晶岩内。
• These pegmatites are characterised by extreme sodium activity, very low silica activity and a high content of volatiles such as chlorine and water.这类伟晶岩以钠活度极高、硅活度极低以及富含氯与水等挥发分为特征。
• It is accompanied at the type locality by eudialyte, nepheline, sodalite, potassic feldspar, arfvedsonite and aegirine.在模式产地，它与异性石、霞石、方钠石、钾长石、铁钠闪石与霓石共生。
• The mineral is rare even within its host pegmatite and forms irregular accumulations rather than well-developed crystals.即便在寄主伟晶岩内该矿物也属稀有，且呈不规则集合体，而非发育良好的晶体。
• Its brightest luminescence under ultraviolet light, a vivid orange-red, is the most practical field aid for recognising the species.在紫外光下呈明亮的橙红色荧光，是该矿物种最实用的野外识别依据。
• The only well-documented locality remains Mount Alluaiv in the Lovozero massif, although closely related modular phases occur elsewhere on the Kola Peninsula.目前唯一有详细记录的产地仍是洛沃泽罗岩体的阿卢瓦伊夫山，不过科拉半岛其他地区也产出相关的模块型物相。

Crystal structure

• Alluaivite is trigonal and crystallises in space group R3̄m, which corresponds to point group 3̄2/m and is the space group of the eudialyte structure type.阿卢瓦石属三方晶系，空间群为 R3̄m，对应点群 3̄2/m，正是异性石结构型的空间群。
• Cell parameters refined from X-ray data are a = 14.046(2) Å and c = 60.60(2) Å, giving a very elongated cell that contains Z = 6 formula units.由 X 射线数据精修的晶胞参数为 a = 14.046(2) Å、c = 60.60(2) Å，晶胞沿 c 轴显著拉长，含 Z = 6 个化学式单位。
• The structure belongs to the modular eudialyte family and is built from twelve-membered silicate rings linked by calcium–sodium polyhedral layers into a framework with large cavities.其结构属模块式异性石族，由十二元硅氧环经钙钠多面体层连接成骨架，骨架内具大型空腔。
• The strong reflections of the powder pattern fall at 2.960 Å (10), 2.825 Å (10), 7.14 Å (8), 1.762 Å (8), 4.30 Å (7) and 2.148 Å (7).粉晶谱的强反射位于 2.960 Å（10）、2.825 Å（10）、7.14 Å（8）、1.762 Å（8）、4.30 Å（7）与 2.148 Å（7）。
• Because the powder pattern closely resembles that of eudialyte, alluaivite can be mistaken for eudialyte in routine X-ray work and requires chemical analysis for confirmation.由于粉晶谱与异性石极为相似，常规 X 射线工作中易将阿卢瓦石误认作异性石，确认须借助化学分析。
• Two other eudialyte-group species, labyrinthite and dualite, contain alluaivite-like modules within their own structures, making the mineral a structural building block for the whole family.异性石族的另外两个矿物种迷宫石与双石，其结构中均含类似阿卢瓦石的模块，因此该矿物可视为整个矿物族的结构构件。

Physical properties

• Alluaivite has a conchoidal fracture and is brittle, and it shows no cleavage.阿卢瓦石具贝壳状断口、性脆，且解理不发育。
• Hardness is 5 to 6 on the Mohs scale, and the measured density of 2.76(5) g/cm³ agrees closely with the calculated value of 2.78 g/cm³.莫氏硬度为 5 至 6，实测密度 2.76(5) g/cm³ 与计算值 2.78 g/cm³ 十分接近。
• Crystals are colourless to weakly brownish pink, transparent, with a white streak and a vitreous lustre.晶体呈无色至浅褐粉色、透明，条痕白色，具玻璃光泽。
• Electron-microprobe analysis of the type material gives SiO₂ 53.3, TiO₂ 6.0, Nb₂O₅ 3.9, MnO 3.6, CaO 8.6, Na₂O 18.6, SrO 1.0, BaO 0.6, Ce₂O₃ 0.8, K₂O 0.2, Cl 0.8 and H₂O 1.7 wt%.模式样品的电子探针分析给出 SiO₂ 53.3、TiO₂ 6.0、Nb₂O₅ 3.9、MnO 3.6、CaO 8.6、Na₂O 18.6、SrO 1.0、BaO 0.6、Ce₂O₃ 0.8、K₂O 0.2、Cl 0.8 与 H₂O 1.7 质量分数。
• The recalculated formula shows substantial substitution, with about 1.5 atoms of manganese and minor strontium, cerium, barium, potassium and zirconium entering the structure.重算后的化学式显示明显类质同象替代，约 1.5 个锰原子以及少量锶、铈、钡、钾与锆进入结构。
• Relative to other eudialyte-group minerals the mineral is titanium-rich and zirconium-poor, with only about 0.2 wt% ZrO₂ in the type analysis.相对于其他异性石族矿物，该矿物富钛贫锆，模式分析中 ZrO₂ 仅约 0.2 质量分数。

Optical properties

• Alluaivite is uniaxial positive, with refractive indices of nω = 1.618(2) and nε = 1.626(2).阿卢瓦石为一轴晶正光性，折射率为 nω = 1.618(2)、nε = 1.626(2)。
• The difference between the two indices, about 0.008, corresponds to very weak birefringence of the same order as the associated eudialyte.两个折射率之差约 0.008，对应与共生异性石同量级的极弱双折射。
• Pleochroism is weak but measurable, with colours ranging from colourless to pink, the pink tone being strongest for the extraordinary ray.多色性弱但可测，颜色由无色至粉色，非常光方向的粉色调最强。
• Under short-wave ultraviolet light the mineral fluoresces a vivid orange-red, a property shared with some other members of the eudialyte group.在短波紫外光下矿物呈明亮橙红色荧光，这一性质与异性石族部分成员相同。
• The refractive indices and the distinctive luminescence together provide a practical means of distinguishing the species from eudialyte in thin section.折射率与特征性发光相结合，为薄片中区分该矿物种与异性石提供了实用手段。

Formation and alteration

• Alluaivite crystallised from an ultra-agpaitic residual melt or associated alkaline fluid at temperatures below those of the main massif crystallisation.阿卢瓦石在低于岩体主体结晶温度的条件下，从超碱性残余熔体或相关碱性流体中结晶。
• The titanium-rich, zirconium-poor bulk composition of the parent pegmatite is the controlling factor that made alluaivite rather than eudialyte the stable phase.母伟晶岩富钛贫锆的整体成分，是使阿卢瓦石而非异性石成为稳定相的控制因素。
• Later hydrothermal overprint in these pegmatites tends to dissolve the mineral and reprecipitate eudialyte-like phases, so fresh material is scarce.这类伟晶岩后期热液叠加往往使该矿物溶解并再沉淀出似异性石的物相，因此新鲜样品稀少。
• The mineral has no recorded weathering products, which reflects the stability of these highly alkaline assemblages at surface conditions.该矿物未见风化产物的报道，这反映了这类高碱性组合在地表条件下的稳定性。

Uses

• Alluaivite has no industrial use, and its grains are far too small and too rare to be cut as gemstones.阿卢瓦石无工业用途，其晶粒过小且极为稀有，无法切磨为宝石。
• Its scientific value lies in the fact that it is the titanium analogue of eudialyte, and the study of its structure underpins the whole modular eudialyte family.其科学价值在于它是异性石的钛类似物，对其结构的研究支撑了整个模块式异性石族。
• Because alluaivite modules appear inside labyrinthite and dualite, the species is a natural reference material for describing modular crystal structures.由于阿卢瓦石模块出现在迷宫石与双石之中，该矿物种是描述模块式晶体结构的天然参照物。
• Specimens are otherwise of interest only to systematic collectors of Kola Peninsula alkaline rocks.除此之外，标本仅对科拉半岛碱性岩的系统收藏者有意义。

Related minerals and varieties

• Alluaivite is a member of the eudialyte group, whose other members, such as eudialyte itself and mogovidite, are zirconosilicates rather than titanosilicates.阿卢瓦石属异性石族，该族的其他成员如异性石与莫戈维德石等，均为锆硅酸盐而非钛硅酸盐。
• Labyrinthite and dualite are the two dual-nature phases that contain both titanium and zirconium and incorporate alluaivite modules in their structures.迷宫石与双石是两个兼具钛与锆的双重性质物相，其结构中包含阿卢瓦石模块。
• Manganese-rich varieties are known, and a related modular titanosilicate with manganese replacing sodium in the alluaivite module was characterised in 2019.该矿物存在富锰变种，2019 年还表征了一种相关的模块式钛硅酸盐，其中锰替代阿卢瓦石模块中的钠。^[1]
• Confusion with eudialyte is the main identification risk, since the two share a space group, a similar cell and almost identical powder patterns.与异性石混淆是主要的鉴定风险，因为两者空间群相同、晶胞相近，粉晶谱几乎一致。
• The known substitution of strontium, cerium, barium and potassium in place of sodium and calcium links the species to the broader alkali-rich eudialyte family chemistry.已知锶、铈、钡与钾可替代钠和钙，这使该矿物种与更广泛的富碱异性石族化学相联系。