Article (Scientific journals)
Jahnsite-(MnMnMg), Mn2þMn2þMg2þ 2Fe3þ 2(PO4)4(OH)28H2O, a new phosphate mineral species from Sapucaia pegmatite, Sapucaia do Norte, Galiléia, Minas Gerais, Brazil
Vignola, P.; Hatert, Frédéric; Baijot, Maxime et al.
2019In Canadian Mineralogist, 57 (3), p. 363-370
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Keywords :
Brazil; Jahnsite group; Jahnsite subgroup; Jahnsite-(MnMnMg); Minas Gerais; New mineral species; Pegmatitic phosphate; Sapucaia; Granite; Phosphate minerals; Crystal structure
Abstract :
[en] Jahnsite-(MnMnMg), Mn2þMn2þMg2þ 2Fe3þ 2(PO4)4(OH)28H2O, is a new phosphate mineral belonging to the jahnsite subgroup contained in the jahnsite group of minerals. It was found in the dumps of the Sapucaia pegmatite, Sapucaia do Norte, Galiléia, Minas Gerais, Brazil by one of the authors (SV). The mineral occurs on the surfaces of hydrothermal cavities and is associated with frondelite, mangangordonite, and leucophosphite. It forms prisms weakly elongated along a, flattened on [010], and twinned by reflection on {001} up to 200 lm in length. The new species is a late stage alteration product of primary phosphates such as triphylite. Its color is yellow to honey-colored or greenish-yellow and it is partially transparent with a vitreous luster. The streak is very pale yellow. Jahnsite-(MnMnMg) is brittle with good cleavage on {001} and irregular fracture. Its inferred Mohs hardness is 4 and the calculated density is 2.625 g/cm3. The mineral is optically biaxial (–) with a ¼ 1.616, b ¼ 1.619, c ¼ 1.656 and 2V (calc.) ¼ 748 and non-fluorescent under 254 nm (short wave) and 366 nm (long wave). The empirical formula is: (Mn0.50Ca0.25Na0.20)R0.95Mn(Mg1.26Mn0.52Fe2þ 0.21Zn0.01)R2(Fe3þ 1.63Al0.37)R2(PO4)4(OH)1.708H2O. The endmember formula is Mn2þMn2þMg2þ 2Fe3þ 2(PO4)4(OH)28H2O. Jahnsite-(MnMnMg) is monoclinic, with space group P2/a and unit-cell parameters a 15.177(2) Å, b 7.176(1) Å, c 10.006(3) Å, and b 110.01(2)8 with V 1017.3(2) Å3 for Z ¼ 2. Its crystal structure was refined and the mineral is isostructural with other members of the jahnsite group. © 2019 Mineralogical Association of Canada. All rights reserved.
Disciplines :
Earth sciences & physical geography
Author, co-author :
Vignola, P.;  CNR-Istituto per la dinamica dei processi ambientali, via Mario Bianco, 9, Milano, I-20131, Italy
Hatert, Frédéric  ;  Université de Liège - ULiège > Département de géologie > Minéralogie et cristallochimie
Baijot, Maxime ;  Université de Liège - ULiège > Département de géologie > Minéralogie et cristallochimie
Rotiroti, N.;  Dipartimento di Scienze della Terra, Università degli Studi di Milano, via Botticelli 23, Milano, I-20133, Italy
Risplendente, A.;  Dipartimento di Scienze della Terra, Università degli Studi di Milano, via Botticelli 23, Milano, I-20133, Italy
Varvello, S.;  Vai De Vit 17, Stresa, 28838, Italy
Language :
English
Title :
Jahnsite-(MnMnMg), Mn2þMn2þMg2þ 2Fe3þ 2(PO4)4(OH)28H2O, a new phosphate mineral species from Sapucaia pegmatite, Sapucaia do Norte, Galiléia, Minas Gerais, Brazil
Publication date :
2019
Journal title :
Canadian Mineralogist
ISSN :
0008-4476
eISSN :
1499-1276
Publisher :
Mineralogical Association of Canada
Volume :
57
Issue :
3
Pages :
363-370
Peer reviewed :
Peer Reviewed verified by ORBi
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since 09 March 2020

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