Potassic-richterite, ideallyAKB(NaCa)CMg5TSi8O22W(OH)2, is recognized as a valid member of the amphibole supergroup (IMA-CNMNC 2017–102). Type material is from the Pajsberg Mn-Fe ore field, Filipstad, Värmland, Sweden, where the mineral occurs in a Mn-rich skarn, closely associated with mainly phlogopite, jacobsite and tephroite. The megascopic colour is straw yellow to grayish brown and the luster vitreous. The nearly anhedral crystals, up to 4 mm in length, are pale yellow (non-pleochroic) in thin section and optically biaxial (−), with α = 1.615(5), β = 1.625(5), γ = 1.635(5). The calculated density is 3.07 g·cm−1. VHN100is in the range 610–946. Cleavage is perfect along 110. EPMA analysis in combination with Mössbauer and infrared spectroscopy yields the empirical formula (K0.61Na0.30Pb0.02)∑0.93(Na1.14Ca0.79Mn0.07)∑2(Mg4.31Mn0.47Fe3+0.20)∑5(Si7.95Al0.04Fe3+0.01)∑8O22(OH1.82F0.18)∑2for a fragment used for collection of single-crystal X-ray diffraction data. The infra-red spectra show absorption bands at 3672 cm−1and 3736 cm−1for the α direction. The crystal structure was refined in space group C2/m to R1 = 3.6% [I > 2σ(I)], with resulting cell parameters a = 9.9977(3) Å, b = 18.0409(4) Å, c = 5.2794(2) Å, γ = 104.465(4)°, V = 922.05(5) Å3and Z = 2. The A and M(4) sites split into A(m) (K+), A(2/m) (Na+), A(2) (Pb2+), and M(4′) (Mn2+) subsites, respectively. The remaining Mn2+is strongly ordered at the octahedrally coordinated M(2) site, possibly together with most of Fe3+. The skarn bearing potassic-richterite formed at peak metamorphism, under conditions of low SiO2and Al2O3activities and relatively high oxygen fugacities.
Description and recognition of potassic-richterite, an amphibole supergroup mineral from the Pajsberg ore field, Värmland, Sweden / D. Holtstam, F. Cámara, H. Skogby, A. Karlsson, J. Langhof. - In: MINERALOGY AND PETROLOGY. - ISSN 0930-0708. - 113:1(2019 Feb 08), pp. 7-16.
|Titolo:||Description and recognition of potassic-richterite, an amphibole supergroup mineral from the Pajsberg ore field, Värmland, Sweden|
CAMARA ARTIGAS, FERNANDO (Secondo) [Writing – Original Draft Preparation]
|Parole Chiave:||Amphibole supergroup; Crystal structure; Långban-type deposit; Pajsberg; Potassic-richterite; Skarn; Sweden; Geophysics; Geochemistry and Petrology|
|Settore Scientifico Disciplinare:||Settore GEO/06 - Mineralogia|
|Data di pubblicazione:||8-feb-2019|
|Data ahead of print / Data di stampa:||10-ago-2018|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1007/s00710-018-0623-6|
|Appare nelle tipologie:||01 - Articolo su periodico|