Ferro-ferri-holmquistite (IMA2022-020), ideal formula
Ferro-ferri-holmquistite (IMA2022-020), ideal formula
Amphibole-supergroup minerals are chemically strongly variable. The standard
amphibole formula is written as AB
The name, ferro-ferri-holmquistite, is based on the nomenclature of the amphibole supergroup (see Table 6 in Hawthorne et al., 2012). The type specimens of ferro-ferri-holmquistite are housed in the National Museum of Nature and Science, Tsukuba, Japan, and the Geological and Mineralogical Museum of Faculty of Science, Yamaguchi University, Japan, under registered numbers NSM-M49617 (holotype) and 95263G (cotype), respectively.
Microphotograph
Small bodies of approximately
The metasomatic rocks in the studied area are classified into the following
types based on the major mineral assemblage, from the initial host rock to the
inner part of metasomatism: (1) the original coarse-grained granite (quartz
Variation of total Fe and Al content (apfu) in ferro-ferri-holmquistite. The number of analytical points equals 52.
Ferro-ferri-holmquistite commonly occurs as acicular aggregates (Fig. 1a)
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
The Gladstone–Dale compatibility index of ferro-ferri-holmquistite was calculated with the measured density (average 3.32 g cm
Chemical composition of ferro-ferri-holmquistite.
The magnetic susceptibility of ferro-ferri-holmquistite from the Iwagi islet is similar to that of the associated biotite determined by mineral separation using a neodymium magnet. It is slightly greater than that of aegirine-augite using a Frantz isodynamic separator at room temperature. Although both ferro-ferri-holmquistite and aegirine-augite were attracted to the magnet at 0.4 A, the former was attracted to the magnet at 0.3 A, but the latter was not.
Chemical tests with hydrochloric acid (HCl), nitrous acid (HNO
Chemical analysis of ferro-ferri-holmquistite was done using an electron
microprobe analyzer (EPMA, JEOL JXA-8230) at Yamaguchi University, Japan,
and laser ablation inductively coupled plasma mass spectrometry
(LA-ICP-MS) at the Japan Agency for Marine-Earth Science and Technology
(JAMSTEC), Japan, following the method of Kimura and Chang (2012). The
chemical composition of ferro-ferri-holmquistite and probe standards are
listed in Table 1. Operating conditions for EMPA were an accelerating voltage
of 15 kV, a beam current of 20 nA and a beam diameter of 1
X-ray powder diffraction data were collected using a Rigaku MiniFlex
automated X-ray powder diffractometer for Cu
Single-crystal X-ray diffraction data (
Single-crystal unpolarized Fourier transmission infrared (FT-IR) spectra
were collected from 700 to 4000 cm
The chemical composition of ferro-ferri-holmquistite is listed in Table 1
with respective standards for elements. Each crystal is slightly zoned (Fig. 1b). Such chemical variability is mainly due to Al
Observed X-ray powder diffraction data (
The observed and simulated powder X-ray diffraction (XRD) pattern of ferro-ferri-holmquistite is
listed in Table 2. The calculated pattern was obtained based on the result
of single-crystal analysis mentioned below. The powder XRD pattern showed
the effect of preferred orientation due to the fibrous and prismatic
crystals. The refined unit-cell parameters from powder data are
Experimental details of the single-crystal X-ray diffraction analysis of ferro-ferri-holmquistite.
Crystallographic data of ferro-ferri-holmquistite are summarized in Table 3.
Structural refinements converged to
Refined atom positions and displacement parameters
(Å
Anisotropic displacement parameters of ferro-ferri-holmquistite.
Crystal structure of ferro-ferri-holmquistite projected
onto (100) showing the configuration of the
Variations of
Variations of the bond-length distortion,
Variation of
Variation of unit-cell parameters against total Fe content (apfu) in holmquistites. Error bars are within the size of symbols. The unit-cell parameters of holmquistite studied by Irusteta and Whittacker (1975) were originally given in Whittaker (1969). The standard deviations were not given in Whittaker (1969).
The OH-stretching FT-IR spectrum (red line) of
ferro-ferri-holmquistite resolved into Gaussian components (broken lines).
Three peaks can be identified in the spectrum, centered at 3614, 3631 and
3644 cm
Site occupancies of ferro-ferri-holmquistite.
Selected bond lengths (Å) and angles
(
Bond-valence analysis (v.u.) of ferro-ferri-holmquistite
weighted on the refined site occupancies
List of orthorhombic lithium amphiboles
The structural formula of ferro-ferri-holmquistite is
According to the structural refinement, the
In our crystal structure, the
The refined occupancies at
The
As shown in Fig. 7, the unit-cell parameters and total Fe content are
positively correlated. The lengthened
Compositional and structural restrictions of holmquistite were discussed by
Cámara and Oberti (2005). In holmquistite, the
Two crystallographically independent OH groups hosted by the oxygen atoms at
O3
The CIF file can be obtained from the corresponding author.
MN designed the project. TI performed the field observations and sample collection. TK performed the observations of optical properties. MN performed and validated the analysis by EPMA, X-ray powder diffraction and X-ray single-crystal diffraction. JK and QC performed the analysis by LA-ICP-MS. TM collected X-ray single-crystal diffraction data. MN and IT discussed all results, and MN wrote the paper.
The contact author has declared that none of the authors has any competing interests.
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We are grateful to the Educational Board of Ehime Prefecture and Kamishima-cho for permission to collect samples. Special thanks are extended to Yuzuru Maki (Rigaku Corporation) for his arrangement to use the RIGAKU HyPix-6000HE, Yoji Morifuku (the Center for Instrumental Analysis, Yamaguchi University) for his technical assistance and Thomas Armbruster for his critical reading of the manuscript. We also thank the chief editor, Sergey Krivovichev, as well as Frank Hawthorne and an anonymous reviewer. One of the authors (Mariko Nagashima) gratefully acknowledges the financial support of Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science, nos. 18K03782 and 20KK0307.
This research has been supported by the Japan Society for the Promotion of Science (grant nos. 18K03782, 20KK0307).
This paper was edited by Sergey Krivovichev and reviewed by Frank Hawthorne and one anonymous referee.