SCRIBNER, Emily D., Jan CEMPÍREK, Lee A. GROAT, R. James EVANS, Cristian BIAGIONI, Ferdinando BOSI, Andrea DINI, Ulf HÅLENIUS, Paolo ORLANDI and Marco PASERO. Magnesio-lucchesiite, CaMg3Al6(Si6O18)(BO3)3(OH)3O, a new species of the tourmaline supergroup. American Mineralogist. Mineralogical Society of America, 2021, vol. 106, No 6, p. 862-871. ISSN 0003-004X. Available from: https://dx.doi.org/10.2138/am-2021-7496.
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Basic information
Original name Magnesio-lucchesiite, CaMg3Al6(Si6O18)(BO3)3(OH)3O, a new species of the tourmaline supergroup
Authors SCRIBNER, Emily D., Jan CEMPÍREK (203 Czech Republic, guarantor, belonging to the institution), Lee A. GROAT, R. James EVANS, Cristian BIAGIONI, Ferdinando BOSI, Andrea DINI, Ulf HÅLENIUS, Paolo ORLANDI and Marco PASERO.
Edition American Mineralogist, Mineralogical Society of America, 2021, 0003-004X.
Other information
Original language English
Type of outcome Article in a journal
Field of Study 10504 Mineralogy
Country of publisher United States of America
Confidentiality degree is not subject to a state or trade secret
WWW URL
Impact factor Impact factor: 3.066
RIV identification code RIV/00216224:14310/21:00119211
Organization unit Faculty of Science
Doi http://dx.doi.org/10.2138/am-2021-7496
UT WoS 000673958300002
Keywords in English Magnesio-lucchesiite; new mineral species; lamprophyre dike; O'Grady Batholith; San Piero in Campo; Elba Island; Lithium; beryllium and boron: Quintessentially crustal
Tags rivok
Tags International impact, Reviewed
Changed by Changed by: doc. Mgr. Jan Cempírek, Ph.D., učo 15719. Changed: 17/9/2021 15:42.
Abstract
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(Mg2.02Fe2+0.62Fe3+0.09Ti0.25V0.01Cr0.01)Σ3.00Z(Al5.31Fe3+0.69⁠)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(Mg1.45Fe2+0.40Al0.79Fe3+0.36⁠)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(Mg2.49Fe2+0.41Ti0.10)Σ3.00Z(Al5.44Fe3+0.46Mg0.09V0.01)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.
Links
GA17-17276S, research and development projectName: Turmalín - indikátor geologických procesů
Investor: Czech Science Foundation
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