Fluoro-edenite from Biancavilla (Catania, Sicily, Italy): Crystal chemistry of a new amphibole end-member
-
Antonio Gianfagna
and
Roberta Oberti
Abstract
Fluoro-edenite, ideally NaCa2Mg5(Si7Al)O22F2, was found both as prismatic or acicular crystals of millimetric size and as fibers in the rock cavities in gray-red altered benmoreitic lavas occurring at Biancavilla (Etnean Volcanic Complex, Catania, Italy). It is associated with feldspars, quartz, clino- and orthopyroxene, fluoro-apatite, ilmenite, and hematite, and probably crystallized from late-stage hydrothermal fluids. Fluoro-edenite is transparent, intense yellow, non-fluorescent, has vitreous to resinous luster, and gives a yellow streak parallel to the c axis; Mohs’ hardness 5-6, Dcalc = 3.09 g/cm3, perfect cleavage on {110}, and conchoidal fracture. In plane-polarized light, fluoro-edenite is birefringent (1st order), biaxial negative, α = 1.6058(5), β = 1.6170(5), γ = 1.6245(5), 2Vcalc = 78.09°, Y ≡ β ⊥ (010), and γ:Z = 26°. No pleochroism is observed. Fluoro-edenite is monoclinic, space group C2/m, a = 9.847(2) Å, b = 18.017(3) Å, c = 5.268(2) Å, β = 104.84(2)°, V = 903.45 Å3, Z = 2; the ten strongest X-ray diffraction lines in the powder pattern are [d(I, hkl)]: 3.125(10, 310), 8.403(6,110), 3.271(5,240), 2.807(4,330), 2.703(3,151), 1.894(2,5̄10), 2.938(2,221), 1.649(2, 461), 3.376(2,131), 1.438(2,6̄61). IR analysis showed absorption bands at 1066, 991, 791, 738, 667, 517, 475 cm-1, and no bands in the OH-stretching region. Structure refinement allowed determination of cation site-preference and ordering. Microprobe analysis of the refined crystal gave SiO2 52.92, TiO2 0.29, Al2O3 3.53, FeOt 2.50, MnO 0.46, MgO 22.65, CaO 10.83, Na2O 3.20, K2O 0.84, F 4.35, Cl 0.07 wt%, and the crystal-chemical formula obtained by combining all the available data is: A(Na0.56 K0.15) B(Na0.30 Ca1.62 Mg0.03 Mn0.05) C(Mg4.68 Fe2+0.19 Fe3+0.10 Ti4+0.03) T(Si7.42 Al0.58) O22O3(F1.98 Cl0.02)2.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- First-principles modeling of the infrared spectrum of kaolinite
- Determination of the limiting fictive temperature of silicate glasses from calorimetric and dilatometric methods: Application to low-temperature liquid volume measurements
- Enthalpies of formation of tremolite and talc by high-temperature solution calorimetry – a consistent picture
- Evidence for an I2/a to Imab phase transition in the silica polymorph moganite at ~570 K
- Thermal decomposition of rhombohedral KClO3 from 29–76 kilobars and implications for the molar volume of fluid oxygen at high pressures
- High-pressure behavior of clinochlore
- Structure and elasticity of wadsleyite at high pressures
- Determination of the fluid–absent solidus and supersolidus phase relationships of MORB-derived amphibolites in the range 4–14 kbar
- F-rich phlogopite stability in ultra-high-temperature metapelites from the Napier Complex, East Antarctica
- Instability of Al2SiO5 “triple-point” assemblages in muscovite+biotite+quartz-bearing metapelites, with implications
- Stability of osumilite coexisting with spinel solid solution in metapelitic granulites at high oxygen fugacity
- Geikielite exsolution in spinel
- Aeromagnetic anomalies, magnetic petrology, and rock magnetism of hemo-ilmenite- and magnetite-rich cumulate rocks from the Sokndal Region, South Rogaland, Norway
- Minor element chemistry of hemo-ilmenite and magnetite in cumulate rocks from the Sokndal Region, South Rogaland, Norway
- Crystal structure analysis of synthetic Ca4Fe1.5Al17.67O32: A high-pressure, spinel-related phase
- Crystal structure of phase X, a high pressure alkali-rich hydrous silicate and its anhydrous equivalent
- Fluoro-edenite from Biancavilla (Catania, Sicily, Italy): Crystal chemistry of a new amphibole end-member
- Description and crystal structure of turtmannite, a new mineral with a 68 Å period related to mcgovernite
- The crystal structure of low melanophlogite
- Crystal structures of Na and K aluminate mullites
- From mastodon ivory to gemstone: The origin of turquoise color in odontolite
- Letters. Elasticity of single-crystal calcite and rhodochrosite by Brillouin spectroscopy
- Ikaite, CaCO3·6H2O: Cold comfort for glendonites as paleothermometers
