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Re-definition, nomenclature and crystal-chemistry of the hellandite group

  • Roberta Oberti EMAIL logo , Giancarlo Della Ventura , Luisa Ottolini , Frank C. Hawthorne and Paola Bonazzi
Published/Copyright: March 28, 2015
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American Mineralogist
From the journal American Mineralogist Volume 87 Issue 5-6

Abstract

Detailed X-ray single-crystal structure refinements and complete (SIMS + EMPA) microprobe chemical analyses of a series of non-metamict samples of hellandite recently found in Latium (Italy), together with a critical re-evaluation of the existing data on hellandite, allow a better understanding of the crystal-chemistry of the hellandite group. Relative to the crystal structure determined by Mellini and Merlino (1977) for a Y-rich sample from Predazzo (Italy), a new tetrahedrally coordinated site has been detected; this may be fully, or in part, occupied by Li and Be. These cations occur at the center of the tetrahedral cavity where the H atom, which is bonded to the O5 O atom, protrudes; thus the H content in hellandite is constrained to values ≤ 2 - (Li + Be + F).

A new general formula for hellandite-group minerals is proposed: X4Y2ZT2[B4Si4O22]W2, where X = Na, Ca, Y, LREE3+ at the eightfold-coordinated M3 and M4 sites; Y = Ca, Y, HREE3+, Th4+, U4+ at the eightfold-coordinated M2 site; Z = Al, Mn3+, Fe3+, Ti4+ at the octahedral M1 site; T = ⃞ (vacancy), Li, Be at the new tetrahedrally coordinated site; and W = OH, F, O2- at the O5 site. Eight root end-member compositions were identified; four of these correspond to known compositions: hellandite-(REE), tadzhikite-(REE), and two new minerals, mottanaite-(Ce) and ciprianiite, which are described in a companion paper (Della Ventura et al. 2002). The root-name tadzhikite must be used for samples with Ti4+ > 0.5 apfu, with no reference to the OH content.

Hellandite is an REE mineral. Rare-earth elements occur at two distinct sites (M2 and M4), with a strong preference for M2 (particularly HREE). Thus, one or two Levinson modifiers can be added to the root name to correctly describe the species. A sequence of incorporation based on crystalchemical arguments is provided and allows evaluation of the site populations for nomenclature purposes.

This redefinition of the hellandite group and the new nomenclature rules have been approved by the IMA Commission on New Minerals and Mineral names (code 00-F).

Received: 2001-6-11
Accepted: 2002-1-30
Published Online: 2015-3-28
Published in Print: 2002-5-1

© 2015 by Walter de Gruyter Berlin/Boston

Articles in the same Issue

  1. Formation of secondary pyrite and carbonate minerals in the Lower Williams Lake tailings basin, Elliot Lake, Ontario, Canada
  2. Hydroxyl in MgSiO3 akimotoite: A polarized and high-pressure IR study
  3. High-pressure IR-spectra and the thermodynamic properties of chloritoid
  4. Infrared and Raman study of interlayer anions CO32–, NO3–, SO42– and ClO4– in Mg/Al-hydrotalcite
  5. Effect of Fe oxidation state on the IR spectra of Garfield nontronite
  6. High-pressure single-crystal X-ray diffraction study of katoite hydrogarnet: Evidence for a phase transition from Ia3d →I4̅3d symmetry at 5 GPa
  7. The high-temperature P21/c-C2/c phase transition in Fe-free pyroxene (Ca0.15Mg1.85Si2O6): Structural and thermodynamic behavior
  8. Thermodynamics and stability of pseudobrookite-type MgTi2O5 (karrooite)
  9. Molecular orbital calculations on aluminosilicate tricluster molecules: Implications for the structure of aluminosilicate glasses
  10. Surface structures, stabilities, and growth of magnesian calcites: A computational investigation from the perspective of dolomite formation
  11. Spinels and other oxides in Mn-rich rocks from the Hutter Mine, Pittsylvania County, Virginia, U.S.A.: Implications for miscibility and solvus relations among jacobsite, galaxite, and magnetite
  12. An occurrence of igneous orthorhombic amphibole, Eriksberg gabbro, southern Sweden
  13. Crystal chemistry of Cr3+-V3+-rich clinopyroxenes
  14. The crystal structures of cesanite and its synthetic analogue—A comparison
  15. Disordered distribution of Cu in the crystal structure of leightonite, K2Ca2Cu(SO4)4 · 2H2O
  16. Neustädtelite and cobaltneustädtelite, the Fe3+ - and Co2+ -analogues of medenbachite
  17. Ciprianiite and mottanaite-(Ce), two new minerals of the hellandite group from Latium (Italy)
  18. Re-definition, nomenclature and crystal-chemistry of the hellandite group
  19. The new mineral baumstarkite and a structural reinvestigation of aramayoite and miargyrite
  20. Letters. Isotopic and elemental partitioning of boron between hydrous fluid and silicate melt
  21. Experimental evidence of three coexisting immiscible fluids in synthetic granitic pegmatite
  22. Quantifying surface areas of clays by atomic force microscopy
  23. A new high-pressure phase of FeSi
https://doi.org/10.2138/am-2002-5-618

Articles in the same Issue

  1. Formation of secondary pyrite and carbonate minerals in the Lower Williams Lake tailings basin, Elliot Lake, Ontario, Canada
  2. Hydroxyl in MgSiO3 akimotoite: A polarized and high-pressure IR study
  3. High-pressure IR-spectra and the thermodynamic properties of chloritoid
  4. Infrared and Raman study of interlayer anions CO32–, NO3–, SO42– and ClO4– in Mg/Al-hydrotalcite
  5. Effect of Fe oxidation state on the IR spectra of Garfield nontronite
  6. High-pressure single-crystal X-ray diffraction study of katoite hydrogarnet: Evidence for a phase transition from Ia3d →I4̅3d symmetry at 5 GPa
  7. The high-temperature P21/c-C2/c phase transition in Fe-free pyroxene (Ca0.15Mg1.85Si2O6): Structural and thermodynamic behavior
  8. Thermodynamics and stability of pseudobrookite-type MgTi2O5 (karrooite)
  9. Molecular orbital calculations on aluminosilicate tricluster molecules: Implications for the structure of aluminosilicate glasses
  10. Surface structures, stabilities, and growth of magnesian calcites: A computational investigation from the perspective of dolomite formation
  11. Spinels and other oxides in Mn-rich rocks from the Hutter Mine, Pittsylvania County, Virginia, U.S.A.: Implications for miscibility and solvus relations among jacobsite, galaxite, and magnetite
  12. An occurrence of igneous orthorhombic amphibole, Eriksberg gabbro, southern Sweden
  13. Crystal chemistry of Cr3+-V3+-rich clinopyroxenes
  14. The crystal structures of cesanite and its synthetic analogue—A comparison
  15. Disordered distribution of Cu in the crystal structure of leightonite, K2Ca2Cu(SO4)4 · 2H2O
  16. Neustädtelite and cobaltneustädtelite, the Fe3+ - and Co2+ -analogues of medenbachite
  17. Ciprianiite and mottanaite-(Ce), two new minerals of the hellandite group from Latium (Italy)
  18. Re-definition, nomenclature and crystal-chemistry of the hellandite group
  19. The new mineral baumstarkite and a structural reinvestigation of aramayoite and miargyrite
  20. Letters. Isotopic and elemental partitioning of boron between hydrous fluid and silicate melt
  21. Experimental evidence of three coexisting immiscible fluids in synthetic granitic pegmatite
  22. Quantifying surface areas of clays by atomic force microscopy
  23. A new high-pressure phase of FeSi
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