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Mejillonesite, a new acid sodium, magnesium phosphate mineral, from Mejillones, Antofagasta, Chile

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Published/Copyright: April 2, 2015
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American Mineralogist
From the journal American Mineralogist Volume 97 Issue 1

Abstract

Mejillonesite, ideally NaMg2(PO3OH)(PO4)(OH)· H5O2, is a new mineral approved by the CNMNC (IMA 2010-068). It occurs as isolated crystal aggregates in thin zones in fine-grained opal-zeolite aggregate on the north slope of Cerro Mejillones, Antofagasta, Chile. Closely associated minerals are bobierrite, opal, clinoptilolite-Na, clinoptilolite-K, and gypsum. Mejillonesite forms orthorhombic, prismatic, and elongated thick tabular crystals up to 6 mm long, usually intergrown in radiating aggregates. The dominant form is pinacoid {100}. Prisms {hk0}, {h0l}, and {0kl} are also observed. The crystals are colorless, their streak is white, and the luster is vitreous. The mineral is transparent. It is non-fluorescent under ultraviolet light. Mohs’ hardness is 4, tenacity is brittle. Cleavage is perfect on {100}, good on {010} and {001}, and fracture is stepped. The measured density is 2.36(1) g/cm3; the calculated density is 2.367 g/cm3. Mejillonesite is biaxial (-), α = 1.507(2), β = 1.531(2), γ = 1.531(2), 2V (meas) = 15(10)°, 2V (calc) = 0° (589 nm). Orientation is X = a, Z = elongation direction. The mineral is non-pleochroic. Dispersion is r > v, medium. The IR spectrum contains characteristic bands of the Zundel cation (H5O2+, or H+·2H2O) and the groups P-OH and OH−. The chemical composition is (by EDS, H2O by the Alimarin method, wt%): Na2O 9.19, MgO 26.82, P2O5 46.87, H2O 19, total 101.88. The empirical formula, based on 11 oxygen atoms, is Na0.93Mg2.08(PO3OH)1.00(PO4)1.06(OH)0.86 · 0.95H5O2. The strongest eight X-ray powder-diffraction lines [d in Å(I)(hkl)] are: 8.095(100)(200), 6.846(9) (210), 6.470(8)(111), 3.317(5)(302), 2.959(5)(132), 2.706(12)(113), 2.157(19)(333), and 2.153(9) (622). The crystal structure was solved on a single crystal (R = 0.055) and gave the following data: orthorhombic, Pbca, a = 16.295(1), b = 13.009(2), c = 8.434(1) Å, V = 1787.9(4) Å3, Z = 8. The crystal structure of mejillonesite is based on a sheet (parallel to the b-c plane) formed by two types of MgO6 octahedra, isolated tetrahedra PO4 and PO3OH whose apical vertices have different orientation with respect to the sheet. The sheets are connected by interlayer, 5-coordinated sodium ions, proton hydration complexes, and hydroxyl groups. The structure of mejillonesite is related to that of angarfite, NaFe53+(PO4)4(OH)4·4H2O and bakhchisaraitsevite, Na2Mg5`(PO4)4·7H2O.

Keywords : Mejillonesite; new mineral; Chile; phosphate
Received: 2011-4-26
Accepted: 2011-9-18
Published Online: 2015-4-2
Published in Print: 2012-1-1

© 2015 by Walter de Gruyter Berlin/Boston

Articles in the same Issue

  1. Boron in natural type IIb blue diamonds: Chemical and spectroscopic measurements
  2. Mejillonesite, a new acid sodium, magnesium phosphate mineral, from Mejillones, Antofagasta, Chile
  3. Silician magnetite from the Dales Gorge Member of the Brockman Iron Formation, Hamersley Group, Western Australia
  4. The mechanism of thermal decomposition of dolomite: New insights from 2D-XRD and TEM analyses
  5. A revised diamond-graphite transition curve
  6. Insights into the crystal and aggregate structure of Fe3+ oxide/silica co-precipitates
  7. Compositional dependence of alkali diffusivity in silicate melts: Mixed alkali effect and pseudo-alkali effect
  8. Kinetics of evaporation of forsterite in vacuum
  9. X-ray absorption near edge structure (XANES) study of the speciation of uranium and thorium in Al-rich CaSiO3 perovskite
  10. Rehydration of dehydrated-dehydroxylated smectite in a low water vapor environment
  11. Effect of high pressure on the crystal structure and electronic properties of magnetite below 25 GPa
  12. OH group behavior and pressure-induced amorphization of antigorite examined under high pressure and temperature using synchrotron infrared spectroscopy
  13. Single-crystal Raman spectroscopy of natural paulmooreite Pb2As2O5 in comparison with the synthesized analog
  14. The dissolution of laumontite in acidic aqueous solutions: A controlled-temperature in situ atomic force microscopy study
  15. Crystal structure of CaRhO3 polymorph: High-pressure intermediate phase between perovskite and post-perovskite
  16. Oxide melt solution calorimetry of Fe2+-bearing oxides and application to the magnetite–maghemite (Fe3O4–Fe8/3O4) system
  17. Static compression of (Mg0.83,Fe0.17)O and (Mg0.75,Fe0.25)O ferropericlase up to 58 GPa at 300, 700, and 1100 K
  18. Implications of ferrous and ferric iron in antigorite
  19. Markascherite, Cu3(MoO4)(OH)4, a new mineral species polymorphic with szenicsite, from Copper Creek, Pinal County, Arizona, U.S.A.
  20. Natural hydrous amorphous silica: Quantitation of network speciation and hydroxyl content by 29Si MAS NMR and vibrational spectroscopy
  21. Lead-tellurium oxysalts from Otto Mountain near Baker, California: VII. Chromschieffelinite, Pb10Te6O20(OH)14(CrO4)(H2O)5, the chromate analog of schieffelinite
  22. Experimental growth of diopside + merwinite reaction rims: The effect of water on microstructure development
  23. Thermodynamic model for growth of reaction rims with lamellar microstructure
  24. The high-pressure behavior of micas: Vibrational spectra of muscovite, biotite, and phlogopite to 30 GPa
  25. Critical evaluation of the revised akdalaite model for ferrihydrite—Discussion
  26. Critical evaluation of the revised akdalaite model for ferrihydrite—Reply
https://doi.org/10.2138/am.2012.3867
Keywords for this article
Mejillonesite; new mineral; Chile; phosphate

Articles in the same Issue

  1. Boron in natural type IIb blue diamonds: Chemical and spectroscopic measurements
  2. Mejillonesite, a new acid sodium, magnesium phosphate mineral, from Mejillones, Antofagasta, Chile
  3. Silician magnetite from the Dales Gorge Member of the Brockman Iron Formation, Hamersley Group, Western Australia
  4. The mechanism of thermal decomposition of dolomite: New insights from 2D-XRD and TEM analyses
  5. A revised diamond-graphite transition curve
  6. Insights into the crystal and aggregate structure of Fe3+ oxide/silica co-precipitates
  7. Compositional dependence of alkali diffusivity in silicate melts: Mixed alkali effect and pseudo-alkali effect
  8. Kinetics of evaporation of forsterite in vacuum
  9. X-ray absorption near edge structure (XANES) study of the speciation of uranium and thorium in Al-rich CaSiO3 perovskite
  10. Rehydration of dehydrated-dehydroxylated smectite in a low water vapor environment
  11. Effect of high pressure on the crystal structure and electronic properties of magnetite below 25 GPa
  12. OH group behavior and pressure-induced amorphization of antigorite examined under high pressure and temperature using synchrotron infrared spectroscopy
  13. Single-crystal Raman spectroscopy of natural paulmooreite Pb2As2O5 in comparison with the synthesized analog
  14. The dissolution of laumontite in acidic aqueous solutions: A controlled-temperature in situ atomic force microscopy study
  15. Crystal structure of CaRhO3 polymorph: High-pressure intermediate phase between perovskite and post-perovskite
  16. Oxide melt solution calorimetry of Fe2+-bearing oxides and application to the magnetite–maghemite (Fe3O4–Fe8/3O4) system
  17. Static compression of (Mg0.83,Fe0.17)O and (Mg0.75,Fe0.25)O ferropericlase up to 58 GPa at 300, 700, and 1100 K
  18. Implications of ferrous and ferric iron in antigorite
  19. Markascherite, Cu3(MoO4)(OH)4, a new mineral species polymorphic with szenicsite, from Copper Creek, Pinal County, Arizona, U.S.A.
  20. Natural hydrous amorphous silica: Quantitation of network speciation and hydroxyl content by 29Si MAS NMR and vibrational spectroscopy
  21. Lead-tellurium oxysalts from Otto Mountain near Baker, California: VII. Chromschieffelinite, Pb10Te6O20(OH)14(CrO4)(H2O)5, the chromate analog of schieffelinite
  22. Experimental growth of diopside + merwinite reaction rims: The effect of water on microstructure development
  23. Thermodynamic model for growth of reaction rims with lamellar microstructure
  24. The high-pressure behavior of micas: Vibrational spectra of muscovite, biotite, and phlogopite to 30 GPa
  25. Critical evaluation of the revised akdalaite model for ferrihydrite—Discussion
  26. Critical evaluation of the revised akdalaite model for ferrihydrite—Reply
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