Ferro-ferri-holmquistite, □Li2(Fe2+3Fe3+2)Si8O22(OH)2, Fe2+Fe3+ analogue of holmquistite, from the Iwagi islet, Ehime, Japan
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Published:2022-10-07
Issue:5
Volume:34
Page:425-438
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ISSN:1617-4011
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Container-title:European Journal of Mineralogy
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language:en
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Short-container-title:Eur. J. Mineral.
Author:
Nagashima MarikoORCID, Imaoka Teruyoshi, Kano Takashi, Kimura Jun-ichi, Chang Qing, Matsumoto Takashi
Abstract
Abstract. Ferro-ferri-holmquistite (IMA2022-020), ideal formula
□Li2(Fe32+Fe23+)Si8O22(OH)2, was
found in albitized granite from the Iwagi islet, Ehime, Japan.
Ferro-ferri-holmquistite is a CFe2+Fe3+ analogue of
holmquistite and belongs to the lithium-subgroup amphiboles. It commonly
occurs as acicular aggregate and/or isolated crystals in quartz, albite and
K-feldspar and is blue with a bluish-grey streak and a vitreous luster. It
has a Mohs hardness of 5 1/2. Its cleavage is perfect on
{210}. Measured and calculated densities are
Dmeas.=3.2 g cm−3 and Dcalc.=3.317 g cm−3,
respectively. Ferro-ferri-holmquistite is optically biaxial (-), with
α=1.685, β=1.713 and γ=1.727, and is
pleochroic, with X= pale blue ∼ pale yellowish blue, Y= deep blue ∼ brownish blue and Z= deep blue ∼ deep bluish violet; X>Z>Y. The magnetic
susceptibility is similar to the associated biotite.
Ferro-ferri-holmquistite is insoluble in HCl, HNO3 and H2SO4.
The empirical formula calculated on the basis of Σ(C+T) = 13 on the results obtained by electron
microprobe analyzer (EPMA), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is
A(K0.01Na0.06)Σ0.07B(Li1.95Na0.04Ca0.01)Σ2.00C(Fe2.822+Fe1.393+Al0.51Mg0.22Mn0.052+Ti0.01)Σ5.00T(Si7.98Al0.02)Σ8.00O22(OH)1.94F0.06. Structure refinement converged
to R1= 4.22 %. The space group is orthorhombic Pnma, and the
unit-cell parameters are a= 18.5437(2) Å, b= 17.9222(1) Å, c= 5.3123(1) Å and V= 1765.51(1) Å3. Based on the refined
site occupancies, the structural formula can be written as
ANa0.062M4(Li1.952Na0.048)Σ2.000M1(Fe1.7702+Mg0.230)Σ2.000M2(Fe1.4463+Fe0.1022+Al0.452)Σ2.000M3(Fe0.8912+Mg0.109)Σ1.000TSi8O22(OH)2 (Z= 4). Three OH-stretching IR
bands, centered at 3614, 3631 and 3644 cm−1, are assigned to the local
configuration M1M1M3= FeFeFe, MgFeFe (including FeMgFe and FeFeMg) and
MgMgFe (including MgFeMg and FeMgMg), respectively, based on the IR studies
of the orthorhombic Pnma amphiboles.
Funder
Japan Society for the Promotion of Science
Publisher
Copernicus GmbH
Subject
Pulmonary and Respiratory Medicine,Pediatrics, Perinatology and Child Health
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