Krásnoite, the fluorophosphate analogue of perhamite, from the Hu

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• journal_title：Mineralogical Magazine
• Contributor：S. J. Mills ; J. Sejkora ; A. R. Kampf ; I. E. Grey ; T. J. Bastow ; N. A. Ball ; P. M. Adams ; M. Raudsepp ; M. A. Cooper
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2012.076.3.13
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：76
• issue：3
• firstpage：625
• section：Articles

摘要

<p id="p-1">Krásnoite is a new mineral (IMA2011-040) from the Huber open pit, Krásno ore district, Czech Republic and the Silver Coin mine, Nevada, USA. Krásnoite is the fluorophosphate analogue of perhamite. Krásnoite occurs as compact to finely crystalline aggregates, balls and rosette-like clusters up to 1 mm across. Individual crystals are platy, show a hexagonal outline and can reach 0.1 mm on edge at Krásno and 0.4 mm at Silver Coin. At both localities, krásnoite occurs very late in phosphaterich paragenetic sequences. Krásnoite crystals are partly transparent with a typically pearly lustre, but can also appear greasy (Krásno) or dull (Silver Coin). The streak is white and the hardness is 5 on the Mohs scale. Crystals are brittle, have an irregular fracture, one imperfect cleavage on {001} and are not fluorescent under SW and LW ultraviolet light. Penetration twinning ⊥ {001} is common. The density for both Krásno and Silver Coin material is 2.48(4) g cmp>−3p>, measured by the sink–float method in an aqueous solution of sodium polytungstate. The calculated density is 2.476 g cmp>−3p> (Krásno). Krásnoite crystals are uniaxial (+), with ω = 1.548(2) and ϵ = 1.549(2) (Krásno) and ω = 1.541(1) and ϵ = 1.543(1) (Silver Coin). The simplified formula of krásnoite is: Ca₃Al_7.7Si₃P₄O_23.5(OH)_12.1F₂·8H₂O. Krásnoite is trigonal, space group P3İm1, with a = 6.9956(4), c = 20.200(2) Å, V = 856.09(9) Åp>3p> and Z = 3. Raman and infrared spectroscopy, coupled with magic-angle spinning nuclear magnetic resonance (MAS–NMR) spectrometry, confirmed the presence of PO₃F, PO₄, SiO₄, H₂O and OH in the crystal structure of krásnoite. p>