Magnesio-lucchesiite, ideally CaMg3Al6(Si6O18)(BO3)3(OH)3O, is a new mineral species of the tourmaline supergroup. The holotype material was discovered within a lamprophyre dike that cross-cuts tourmaline-rich metapelites within the exocontact of the O’Grady Batholith, Northwest Territories (Canada). Two additional samples were found at San Piero in Campo, Elba Island, Tuscany (Italy) in hydrothermal veins embedded in meta-serpentinites within the contact aureole of the Monte Capanne intrusion. The studied crystals of magnesio-lucchesiite are black in a hand sample with vitreous luster, conchoidal fracture, an estimated hardness of 7–8, and a calculated density of 3.168 (Canada) and 3.175 g/cm3 (Italy). In plane-polarized light, magnesio-lucchesiite is pleochroic (O = dark brown, E = colorless) and uniaxial (–); its refractive index values are nω = 1.668(3) and nε = 1.644(3) (Canada), and nω = 1.665(5) and nε = 1.645(5) (Italy). Magnesio-lucchesiite is trigonal, space group R3m, Z = 3, with a = 15.9910(3) Å, c = 7.2224(2) Å, V = 1599.42(7) Å3 (Canada) and with a = 15.9270(10) Å, c = 7.1270(5) Å, V = 1565.7(2) Å3 (Italy, sample 1). The crystal structure of magnesio-lucchesiite was refined to R1 = 3.06% using 2953 reflections with Fo > 4σ(Fo) (Canadian sample; 1.96% / 1225 for the Italian sample) The Canadian (holotype) sample has the ordered empirical formula X(Ca0.60Na0.39K0.01)Σ1.00Y(Mg2.02Fe0.622+Fe0.093+Ti0.25V0.01Cr0.01)Σ3.00Z(Al5.31Fe0.693+⁠)Σ6.00[T(Si5.98Al0.02)Σ6.00O18](BO3)3V[(OH)2.59O0.41]Σ3.00W(O0.78F0.22)Σ1.00. The Italian (co-type) material shows a wider chemical variability, with two different samples from the same locality having ordered chemical formulas: X(Ca0.88Na0.12)Σ1.00Y(Mg1.45Fe0.402+Al0.79Fe0.363+⁠)Σ3.00ZAl6[T(Si5.05Al0.95)Σ6.00O18](BO3)3V[(OH)2.90O0.10]Σ3.00W(O0.98F0.02)Σ1.00 (sample 1) and X(Ca0.71Na0.21☐0.08)Σ1.00Y(Mg2.49Fe0.412+Ti0.10)Σ3.00Z(Al5.44Fe0.463+Mg0.09V0.01)Σ6.00[T(Si5.87Al0.13)Σ6.00O18](BO3)3V(OH)3W[O0.61(OH)0.39]Σ1.00 (sample 2). Magnesio-lucchesiite is an oxy-species belonging to the calcic group of the tourmaline supergroup. It is related to lucchesiite by the homovalent substitution YFe ↔ YMg, and to feruvite by the homovalent and heterovalent substitutions YFe ↔ YMg and ZAl3+ + WO2– ↔ ZMg2+ + W(OH)1–. The new mineral was approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA 2019-025). Occurrences of magnesio-lucchesiite show that its presence is not restricted to replacement of mafic minerals only; it may also form in metacarbonate rocks by fluctuations of F and Al during crystallization of common uvitic tourmaline. High miscibility with other tourmaline end-members indicates the large petrogenetic potential of magnesio-lucchesiite in Mg, Al-rich calc-silicate rocks, as well as contact-metamorphic and metasomatic rocks.

中文翻译：

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Magnesio-lucchesiite，CaMg3Al6(Si6O18)(BO3)3(OH)3O，电气石超群的新物种

Magnesio-lucchesiite，理想情况下是 CaMg3Al6(Si6O18)(BO3)3(OH)3O，是电气石超群的一种新矿物。正模材料是在一个菱形岩脉中发现的，该岩脉在西北地区（加拿大）O'Grady Batholith 的外接触面内横切富含碧玺的变泥质岩。在意大利托斯卡纳厄尔巴岛坎波的圣皮耶罗 (San Piero) 发现了另外两个样本，这些样本位于 Monte Capanne 侵入体接触光环内嵌入变蛇纹岩中的热液脉中。所研究的镁锌矿晶体在手样品中呈黑色，具有玻璃光泽、贝壳状断裂、估计硬度为 7-8，计算密度为 3.168（加拿大）和 3.175 g/cm3（意大利）。在平面偏振光下，镁光石是多向色性的（O = 深棕色，E = 无色）和单轴 (-)；其折射率值为 nω = 1.668(3) 和 nε = 1.644(3)（加拿大），nω = 1.665(5) 和 nε = 1.645(5)（意大利）。Magnesio-lucchesiite 是三角形的，空间群 R3m，Z = 3，a = 15.9910(3) Å，c = 7.2224(2) Å，V = 1599.42(7) Å3（加拿大），a = 15.9270(10) Å , c = 7.1270(5) Å, V = 1565.7(2) Å3（意大利，样本 1）。使用 2953 次反射，Fo > 4σ(Fo)（加拿大样品；意大利样品为 1.96% / 1225） 加拿大（正模）样品具有有序经验公式 X( Ca0.60Na0.39K0.01)Σ1.00Y(Mg2.02Fe0.622+Fe0.093+Ti0.25V0.01Cr0.01)Σ3.00Z(Al5.31Fe0.693+⁠)Σ6.00[T(Si5. 98Al0.02)Σ6.00O18](BO3)3V[(OH)2.59O0.41]Σ3.00W(O0.78F0.22)Σ1.00。意大利（共型）材料显示出更广泛的化学变异性，来自同一地点的两个不同样品具有有序的化学式：X(Ca0.88Na0.12)Σ1.00Y(Mg1.45Fe0.402+Al0.79Fe0.363+⁠)Σ3.00ZAl6[T(Si5.05Al0.95) )Σ6.00O18](BO3)3V[(OH)2.90O0.10]Σ3.00W(O0.98F0.02)Σ1.00（样品1）和X(Ca0.71Na0.21☐0.08)Σ1.00Y( Mg2.49Fe0.412+Ti0.10)Σ3.00Z(Al5.44Fe0.463+Mg0.09V0.01)Σ6.00[T(Si5.87Al0.13)Σ6.00O18](BO3)3V(OH)3W [O0.61(OH)0.39]Σ1.00（样品 2）。Magnesio-lucchesiite 是一种含氧物质，属于电气石超群的钙质群。它通过同价取代 YFe ↔ YMg 与铁锌矿相关，通过同价和异价取代 YFe ↔ YMg 和 ZAl3+ + WO2– ↔ ZMg2+ + W(OH)1– 与铁镁矿相关。新矿物获得了国际矿物学协会新矿物、命名和分类委员会 (IMA 2019-025) 的批准。镁锌矿的出现表明它的存在不仅限于替代镁铁矿；它也可能在常见的葡萄石电气石结晶过程中通过 F 和 Al 的波动在偏碳酸盐岩石中形成。与其他电气石端元的高混溶性表明镁-镁铝榴石在富含镁、铝的钙硅酸盐岩以及接触变质和交代岩中具有巨大的成岩潜力。