Abuite

Abuite is a rare calcium aluminium phosphate mineral that forms colourless grains in hydrothermally altered volcanic rocks at a single locality in Japan.阿布伊特是一种稀有的钙铝磷酸盐矿物，在日本一处产地呈无色晶粒产于热液蚀变火山岩中。

It was approved as a new mineral species in 2014 and formally described in 2017, and its name refers to the Abu district of Yamaguchi Prefecture where it was discovered.它于 2014 年获批为新矿物种、2017 年正式描述，名称取自发现地山口县阿布地区。

Because the grains rarely exceed 500 μm and are optically almost indistinguishable from the quartz and augelite that enclose them, abuite is known almost entirely from microscopic material.由于晶粒很少超过 500 μm，且与包裹它的石英和光彩石在光学上几乎无法区分，阿布伊特几乎全部来自显微级材料。

Discovery and naming

• Abuite was discovered in hydrothermally altered rocks at the Hinomaru–Nago mine, Kiyo area, Abu, Abu County, Yamaguchi Prefecture, Japan, at 34°53′N 131°52′E.阿布伊特发现于日本山口县阿布郡阿布町木与地区日之丸—那古矿的热液蚀变岩石中，坐标为北纬 34°53′、东经 131°52′。
• The mineral was recognised as new in 2014 and registered by the IMA Commission on New Minerals, Nomenclature and Classification under the number IMA 2014-084.该矿物于 2014 年被确认为新矿物种，由国际矿物学协会新矿物及矿物命名委员会以编号 IMA 2014-084 登记。
• The type description was published by Satomi Enju and Seiichiro Uehara in 2017, in volume 112 of the Journal of Mineralogical and Petrological Sciences.其模式描述由円珠理美与上原誠一郎于 2017 年发表于《矿物学与岩石学杂志》第 112 卷。^[1]
• The name honours the type locality rather than a person: Abu, the town and county in western Honshu that produced the first specimens.命名取自模式产地而非人名，即出产首批标本的本州西部阿布郡阿布町。
• Type material is curated at the Kitakyushu Museum of Natural History and Human History in Japan, under catalogue number KMNHM000003.模式标本保存在日本北九州市立自然史与历史博物馆，编号 KMNHM000003。

Occurrence and paragenesis

• Abuite occurs in hydrothermally altered felsic pyroclastic rocks that were metamorphosed and metasomatised around a biotite adamellite intrusion.阿布伊特产于酸性火山碎屑岩中，这些岩石在黑云母石英二长岩侵入体周围经历了热液蚀变与交代作用。
• At the type locality it is embedded in aluminium-phosphate-rich nodules together with quartz and augelite and/or trolleite.在模式产地，它与石英及光彩石或车石共生，嵌布于富铝磷酸盐结核中。
• It is accompanied by other phosphates, most notably apatite and crandallite.它常伴随其他磷酸盐出现，尤以磷灰石与钙磷铝石最为常见。
• Field identification is impractical because the dominant associated phases — quartz, augelite and trolleite — are themselves transparent and colourless.野外鉴定极为困难，因为主要共生矿物石英、光彩石与车石本身也都是透明无色的。
• No confirmed occurrence outside the Hinomaru–Nago mine has been reported, which makes abuite one of the many single-locality aluminium phosphates.除日之丸—那古矿外尚无确证产地，这使阿布伊特成为众多单一产地铝磷酸盐之一。
• It is chemically related to galliskiite, differing chiefly in that abuite is hydrated.它在化学上与加里斯凯石相近，主要差别在于阿布伊特是含水的。
• The extreme rarity reflects a narrow window of conditions: a fluorine-bearing, aluminium-rich hydrothermal fluid reacting at low temperature with a calcium-bearing, siliceous host.其极度稀有反映了成因条件的狭窄窗口，即含氟富铝热液在低温下与含钙硅质围岩反应。

Crystal structure

• Abuite is orthorhombic and crystallises in space group P2₁2₁2₁, which corresponds to point group 222.阿布伊特属正交晶系，空间群为 P2₁2₁2₁，对应点群 222。
• Unit-cell parameters refined from the X-ray diffraction pattern are a = 11.818(2) Å, b = 11.993(3) Å and c = 4.6872(8) Å, giving a cell volume of 664.3(2) ų with Z = 4.由 X 射线衍射图谱精修的晶胞参数为 a = 11.818(2) Å、b = 11.993(3) Å、c = 4.6872(8) Å，晶胞体积 664.3(2) ų，Z = 4。
• The natural grains are too small for single-crystal structural refinement, so the cell and space group were derived from powder data by analogy with the isostructural synthetic compound SrAl₂(PO₄)₂F₂.天然晶粒过小，无法进行单晶结构精修，故晶胞与空间群由粉晶数据参照同构的人工合成物 SrAl₂(PO₄)₂F₂ 推出。
• In that isostructural analogue, AlO₆ octahedra and PO₄ tetrahedra share corners to build a three-dimensional framework enclosing channels that accommodate the large cations and fluorine.在该同构类似物中，AlO₆ 八面体与 PO₄ 四面体共角相连构成三维骨架，骨架孔道容纳大半径阳离子与氟。
• The strongest reflections of the X-ray powder pattern occur at 2.951 Å (100), 3.139 Å (86), 2.928 Å (80), 3.529 Å (43) and 3.683 Å (32).X 射线粉晶谱中最强反射位于 2.951 Å（100）、3.139 Å（86）、2.928 Å（80）、3.529 Å（43）与 3.683 Å（32）。
• Abuite is the calcium analogue of the hydrothermally synthesised strontium member, and the two phases are expected to be fully isotypic.阿布伊特是热液合成的锶端元的钙类似物，两者预期完全同型。

Physical properties

• Cleavage has not been observed in abuite, and tenacity and fracture could not be measured on grains of this size.阿布伊特未见解理，且因晶粒过小，韧性与断口均无法测定。
• The density was calculated at 3.214 g/cm³ and no measured value exists, because the grains are far too small for suspension weighing.密度计算值为 3.214 g/cm³，由于晶粒远小于悬浮称重所需尺寸，故无实测值。
• Grains reach about 500 μm, and aggregates intergrown with the host phosphate minerals reach 2 mm.单晶粒约可达 500 μm，与围岩磷酸盐矿物互生的集合体可达 2 mm。
• Twenty-one electron-microprobe analyses give P₂O₅ 45.04, Al₂O₃ 31.26, CaO 17.29, SrO 0.22 and F 11.24 wt%, with water calculated from stoichiometry.21 个电子探针分析给出 P₂O₅ 45.04、Al₂O₃ 31.26、CaO 17.29、SrO 0.22 与 F 11.24 质量分数，含水量按化学计量比计算。
• On the basis of ten anions per formula unit the empirical formula is (Ca₀.₉₉Sr₀.₀₁)Al₁.₉₆P₂.₀₃O₈(F₁.₈₉OH₀.₁₁).以每个化学式单位十个阴离子为基准，其经验式为 (Ca₀.₉₉Sr₀.₀₁)Al₁.₉₆P₂.₀₃O₈(F₁.₈₉OH₀.₁₁)。
• Strontium partly replaces calcium, reaching 5.39 wt% SrO in one of the analysed samples, and the hydrated end is correspondingly fluorine-poor.锶可部分替代钙，在其中一个分析样品中 SrO 达 5.39 质量分数，相应地含水端元含氟较低。
• The mineral is colourless, transparent, with a white streak and a vitreous lustre, and no fluorescence was detected under ultraviolet light.矿物无色透明，条痕白色，具玻璃光泽，在紫外光下未检出荧光。

Optical properties

• No refractive indices have been published, because the handful of available grains is too small for immersion methods or spindle-stage measurement.该矿物尚无折射率发表，因为可获得的晶粒极少且过小，无法进行油浸法或旋转台测量。
• Consequently no optical class has been assigned, and the type description states explicitly that optical data must await larger crystals.因此其光学类别尚未确定，模式描述明确指出光学数据须等待发现更大晶体后补充。
• The mineral is isotropic in appearance only because of its small grain size, and by analogy with the strontium compound it should be birefringent.矿物外观上的均质性仅源于晶粒细小，参照锶类似物它应具有双折射。
• Abuite is transparent in thin section and shows no pleochroism, and its calculated mean refractive index is consistent with a calcium aluminium phosphate framework.阿布伊特在薄片中透明、无多色性，其计算平均折射率与钙铝磷酸盐骨架相符。
• Opaque inclusions of iron and manganese oxides, common in the altered host rock, are the main optical complication when the mineral is studied in polished section.蚀变围岩中常见的铁锰氧化物不透明包裹体，是镜下研究该矿物时的主要光学干扰。

Formation and alteration

• Abuite crystallised from low-temperature hydrothermal fluids that had leached aluminium, phosphorus and fluorine from the surrounding pyroclastic rocks.阿布伊特从低温热液中结晶，这些热液从周围火山碎屑岩中淋滤出铝、磷和氟。
• The association with augelite, trolleite and crandallite places it in the late, low-temperature stage of the aluminium-phosphate paragenesis.它与光彩石、车石和钙磷铝石的共生关系，将其定位在铝磷酸盐生成序列的晚期低温阶段。
• Its fluorine content and its hydrated character indicate precipitation from a fluid that was F-rich but also relatively cool and near-neutral.其含氟与含水的特征表明，它沉淀自一种富氟但温度较低且近中性的流体。
• No alteration products have been documented, which is consistent with the mineral's stability under the ambient conditions of the deposit.目前未见蚀变产物的报道，这与该矿物在矿床现今环境条件下的稳定性相符。

Uses

• Abuite has no industrial or economic use: it is known from a single locality and from grains of microscopic size.阿布伊特无工业或经济用途，其已知产地仅一处，且晶粒仅为显微级。
• Its significance is scientific, because it is the natural calcium member of a structural family previously known only from hydrothermal synthesis.其价值在于科学意义，因为它是此前仅见于人工水热合成的结构族中的天然钙端元。
• For collectors the species is essentially unobtainable outside research collections, since the crystals cannot be picked out by eye from the enclosing quartz.对收藏者而言，该矿物种在研究收藏之外几乎无法获得，因为晶体无法凭肉眼从伴生石英中挑出。

Related minerals and varieties

• Abuite belongs to the small family of anhydrous and hydrated aluminium phosphates that includes augelite, trolleite, crandallite and gatumbaite.阿布伊特属于无水与含水铝磷酸盐小家族，成员包括光彩石、车石、钙磷铝石与加通巴石。
• Galliskiite is its closest chemical relative, and the two differ mainly in the degree of hydration.加里斯凯石是其在化学上最相近的矿物，两者主要差异在于水化程度。
• The synthetic strontium analogue SrAl₂(PO₄)₂F₂ is isostructural and supplied the structural model used for abuite.人工合成的锶类似物 SrAl₂(PO₄)₂F₂ 与之同构，为阿布伊特提供了所用的结构模型。
• Confusion with augelite and trolleite in the field is inevitable, and identification requires electron-microprobe analysis or X-ray diffraction.在野外必然与光彩石和车石混淆，鉴定须借助电子探针分析或 X 射线衍射。
• The strontium-rich grains, locally reaching 5 wt% SrO, form a limited solid solution towards a hypothetical SrAl₂(PO₄)₂F₂ end member.富锶晶粒局部 SrO 可达 5 质量分数，构成向假想端元 SrAl₂(PO₄)₂F₂ 的有限固溶体系列。