Edgrewite Ca9(SiO4)4F2-hydroxyledgrewite Ca9(SiO4)4(OH)2, a new series of calcium humite-group minerals from altered xenoliths in the ignimbrite of Upper Chegem caldera, Northern Caucasus, Kabardino-Balkaria, Russia

Abstract

Members of the edgrewite Ca 9 (SiO 4 ) 4 F 2 -hydroxyledgrewite Ca 9 (SiO 4 ) 4 (OH) 2 series, structural analogues of clinohumite-hydroxylclinohumite series, Mg 9 (SiO 4 ) 4 (F,OH) 2 , were discovered in xenoliths of carbonate-silicate rock altered to skarn within ignimbrites of the Upper Chegem volcanic structure, Kabardino-Balkaria, Northern Caucasus, Russia. The new minerals occur sparingly in zones containing bultfonteinite, hillebrandite, jennite, and chegemite, as well as rare relics of larnite and rondorfite enclosed in a matrix of hydroxylellestadite. Edgrewite and hydroxyledgrewite are largely altered to jennite in places with admixed zeophyllite and trabzonite, and are preserved as elongate relics mostly 0.1-0.4 mm long in the central part of atoll-like pseudomorphs. The new minerals form a solid-solution series Ca 9 (SiO 4 ) 4 (F,OH) 2 , in which the content of the edgrewite end-member Ca 9 (SiO 4 ) 4 F 2 ranges from 74% (F = 3.64 wt%) to 31% (F = 1.52 wt%).Structure refinement of crystals containing 51% and 37% of the edgrewite end-member gave, respectively, R 1 = 3.03%, space group P2 1 /b11 (no. 14), Z = 2, a = 5.06870(10), b = 11.35790(10), c = 15.4004(2) Å, α = 100.5980(10)°, V = 871.47(3) Å 3 ; and R 1 = 1.61%, space group P2 1 /b11 (no. 14), Z = 2, a = 5.06720(10), b = 11.35450(10), c = 15.3941(2) Å, α = 100.5870(10)°, and V = 870.63(2) Å 3 .Minerals of the edgrewite-hydroxyledgrewite series are colorless, optically biaxial (+), 2V meas = 80(5)°; 2V calc = 78.7°; dispersion r > v, medium; orientation: Z = a, X ∧ c = 12(2)°; edgrewite: α = 1.621(2), β = 1.625(2), γ = 1.631(2); hydroxyledgrewite: α = 1.625(2), β = 1.629(2), γ = 1.635(2) (589 nm). The micro-hardness VHN 50 = 352-366 kg/mm 2 corresponds to the Mohs scale of 5.5-6. 5. FTIR spectra of edgrewite and hydroxyledgrewite show resolved bands at (edgrewite/hydroxyledgrewite, cm -1 ): 3558 and 3551 and 3543/3554, absent/3486, 1075/1075, 996/996, 980/982, 934/933, 917/918, 904/903, 890/884, 864/864, 842/842, 818/820. Raman spectra are characterized by the following bands (edgrewite/hydroxyledgrewite, cm -1 ) at: 921/923, 889/890, 839/840, and 815/814 (SiO 4 stretching), at: 556/559, 527/527, 423/419, 406/404, and 394/394 (SiO 4 bending), 309/295, 269/256, and 163/166 (CaO 6 ). In the OH stretching region three bands are noted at 3554, 3547, and 3540 cm -1 for edgrewite and two -3550 and 3475 cm -1 for hydroxyledgrewite confirming the corresponding IR spectra. The major difference in Raman and IR spectra of edgrewite and hydroxyledgrewite is the presence of two resolved peaks in the OH stretching region at ca. 3550 and 3480 cm -1 for hydroxyledgrewite.

Sharyginite, Ca3TiFe2O8, A New Mineral from the Bellerberg Volcano, Germany

“…Mostly, they are characterized by the presence of wadalite inclusions (Figure 5b). rusinovite, Ca10(Si2O7)3Cl2 [22], pavlovskyite, Ca8(SiO4)2(Si3O10) [23], edgrewite, Ca9(SiO4)4F2 [24], dzhuluite, Ca3SbSnFe 3+ 3O12 [25], etc. More geological information concerning this locality can be found in Gazeev et al [18], Galuskin et al [8,20] and Galuskina et al [26].…”

Chirvinskyite, (Na,Ca)13(Fe,Mn,□)2(Ti,Nb)2(Zr,Ti)3-(Si2O7)4(OH,O,F)12, a New Mineral with a Modular Wallpaper Structure, from the Khibiny Alkaline Massif (Kola Peninsula, Russia)

“…The intensive bands at 607, 636s, and 652 as well as 330, 347w, 413w, and 445 cm −1 can be assigned to the Si-O-Si and O-Si-O asymmetric and symmetric modes of bending vibrations in the [Si 2 O 7 ]-groups. The bands observed in the ranges of 900 to 1000 and 700 to 850 cm −1 can be related to the asymmetric and symmetric vibrations of the same bonds[20,21]. The bands at 481s, 497, 538, 593, 177, and 196 cm −1 are assigned to the bending and stretching vibrations of the Ti-O, Zr-O, Mn-O, and Fe-O bonds in respective cation-centered octahedra [22,23].…”

Part 1: A study on the properties of synthetic hydroxyledgrewite

“…SEM was applied for visual inspection of surface morphology (texture) and crystalline structure. According Galuskin et al, the natural hydroxyledgrewite mineral showed combinations of pinacoids and rhombic prisms. Meanwhile SEM micrographs of synthetic hydroxyledgrewite showed irregular form particles with average size 2‐6 μm (Figure A,B).…”

“…Hydroxyledgrewite (Ca 9 (SiO 4 ) 4 (OH) 2 ) is dibasic calcium silicate hydrate (C/S‐2.25), and as α‐C 2 SH belong to nesosilicates or orthosilicates group; these silicates possess the lowest degree of polymerization possible, namely CSH phases with isolated silicon tetrahedra (Q0) . Hydroxyledgrewite was first discovered in 2009, approved by CNMNC IMA in March of 2012 and named in honor of Edward S. Grew, a well‐known scientist in the areas of mineralogy and petrology . Galuskin et al also described physical and optical properties, chemical composition and crystal structure of natural edgrewite and hydroxyledgrewite.…”

“…Hydroxyledgrewite was first discovered in 2009, approved by CNMNC IMA in March of 2012 and named in honor of Edward S. Grew, a well‐known scientist in the areas of mineralogy and petrology . Galuskin et al also described physical and optical properties, chemical composition and crystal structure of natural edgrewite and hydroxyledgrewite.…”