Synthetic Ag-rich tourmaline: Structure and chemistry
-
David London
,
Andreas Ertl
Abstract
Ag-rich tourmaline crystals were synthesized at 750 °C, 200 MPa H2O, and fO₂ = log (NNO) - 0.5, starting with an oxide mix of dravite composition to which various reagents, including AgF and AgCl, were added. Tourmaline containing up to 7.65 wt% Ag2O was synthesized, and this is the first time a tourmaline is described that contains significant amounts of Ag at the ninefold-coordinated X site. Crystal structure refinement and chemical analysis (EMPA) give the optimized formula X(Na0.58Ag0.18□0.24) Y(Al1.54Mg1.46) Z(Al5.34Mg0.66) T(Si5.90Al0.10)O18 (BO3)3V(OH)3W(O0.53F0.47), with a = 15.8995(4) and c = 7.1577(4) Å, and R = 0.036 for a crystal (~20 × 100 μm) with approximately 2.2 wt% Ag2O. Refining Na ↔ Ag at the X site clearly indicates that Ag occupies this site. The X-O2 distance of ~2.52 Å is slightly longer than tourmaline with ~(Na0.6□0.4), reflecting the slightly larger ionic radius of Ag compared to Na. Releasing the occupancy at the Y site gives ~Al0.98 (~12.7 e.), which can be explained by occupation of Mg and Al. On a bond-angle distortion vs. <Y-O> distance diagram, the Ag-rich olenite- dravite lies approximately on the V site = 3 (OH) line in the figure, defining the relation between bond-angle distortion (σoct2) of the ZO6 octahedron and the <Y-O> distance. No H could be found at the O1 site by refinement, in agreement with the Mg-Al disorder between the Y site and the Z site. Synthetic tourmaline contains no Ag when only AgCl is added; the compatibility of Ag in tourmaline, therefore, is largely a function of the F/Cl ratio of the fluid medium. A positive association of Ag at the X site with Al at the Y site and with F suggests that tourmaline might be useful for exploration in Cornwall-type polymetallic ore deposits associated with F-rich peraluminous granites or at other Ag-, F-, and B-enriched deposits such as Broken Hill, Australia. Preliminary electron microprobe analyses of tourmaline from Cornwall and Broken Hill, however, failed to detect Ag at the 3σ detection level of 0.08 wt% Ag2O.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- Structural model for the biogenic Mn oxide produced by Pseudomonas putida
- Electron-beam (5–10 keV) damage in triplite-group phosphates: Consequences for electron-microprobe analysis of fluorine
- Vacancy defects in MgO at high pressure
- Plastic flow of pyrope at mantle pressure and temperature
- Parvo-mangano-edenite, parvo-manganotremolite, and the solid solution between Ca and Mn2+ at the M4 site in amphiboles
- Reinvestigation of the MgSiO3 perovskite structure at high pressure
- The mechanism and kinetics of α-NiS oxidation in the temperature range 670–700°C
- Influence of charge location on 29Si NMR chemical shift of 2:1 phyllosilicates
- The size distribution of exsolution lamellae in iron-free clinopyroxene
- The high-pressure phase transformation and breakdown of MgFe2O4
- Elastic behavior, phase transition, and pressure induced structural evolution of analcime
- A new chemical etching technique for peridotites using molten anhydrous borax
- Poppiite, the V3+ end-member of the pumpellyite group: Description and crystal structure
- Cation redistribution in the octahedral sheet during diagenesis of illite-smectites from Jurassic and Cambrian oil source rock shales
- A shock-induced polymorph of anatase and rutile from the Chesapeake Bay impact structure, Virginia, U.S.A.
- Water in the interlayer region of birnessite: Importance in cation exchange and structural stability
- In situ HAFM study of the thermal dehydration on gypsum (010) surfaces
- Influence of dehydration kinetics on T-O-T bridge breaking in zeolites with framework type STI: The case of stellerite
- Estimation of volume fractions of liquid and vapor phases in fluid inclusions, and definition of inclusion shapes
- Thermodynamics of uranyl minerals: Enthalpies of formation of uranyl oxide hydrates
- SIMS investigation of electron-beam damage to hydrous, rhyolitic glasses: Implications for melt inclusion analysis
- Synthetic Ag-rich tourmaline: Structure and chemistry
- Genesis and compositional heterogeneity of smectites. Part III: Alteration of basic pyroclastic rocksA case study from the Troodos Ophiolite Complex, Cyprus
- Ganterite, the barium mica Ba0.5K0.5Al2(Al1.5Si2.5)O10(OH)2, from Oreana, Nevada
- Letter. Transformation of pentlandite to violarite under mild hydrothermal conditions
Articles in the same Issue
- Structural model for the biogenic Mn oxide produced by Pseudomonas putida
- Electron-beam (5–10 keV) damage in triplite-group phosphates: Consequences for electron-microprobe analysis of fluorine
- Vacancy defects in MgO at high pressure
- Plastic flow of pyrope at mantle pressure and temperature
- Parvo-mangano-edenite, parvo-manganotremolite, and the solid solution between Ca and Mn2+ at the M4 site in amphiboles
- Reinvestigation of the MgSiO3 perovskite structure at high pressure
- The mechanism and kinetics of α-NiS oxidation in the temperature range 670–700°C
- Influence of charge location on 29Si NMR chemical shift of 2:1 phyllosilicates
- The size distribution of exsolution lamellae in iron-free clinopyroxene
- The high-pressure phase transformation and breakdown of MgFe2O4
- Elastic behavior, phase transition, and pressure induced structural evolution of analcime
- A new chemical etching technique for peridotites using molten anhydrous borax
- Poppiite, the V3+ end-member of the pumpellyite group: Description and crystal structure
- Cation redistribution in the octahedral sheet during diagenesis of illite-smectites from Jurassic and Cambrian oil source rock shales
- A shock-induced polymorph of anatase and rutile from the Chesapeake Bay impact structure, Virginia, U.S.A.
- Water in the interlayer region of birnessite: Importance in cation exchange and structural stability
- In situ HAFM study of the thermal dehydration on gypsum (010) surfaces
- Influence of dehydration kinetics on T-O-T bridge breaking in zeolites with framework type STI: The case of stellerite
- Estimation of volume fractions of liquid and vapor phases in fluid inclusions, and definition of inclusion shapes
- Thermodynamics of uranyl minerals: Enthalpies of formation of uranyl oxide hydrates
- SIMS investigation of electron-beam damage to hydrous, rhyolitic glasses: Implications for melt inclusion analysis
- Synthetic Ag-rich tourmaline: Structure and chemistry
- Genesis and compositional heterogeneity of smectites. Part III: Alteration of basic pyroclastic rocksA case study from the Troodos Ophiolite Complex, Cyprus
- Ganterite, the barium mica Ba0.5K0.5Al2(Al1.5Si2.5)O10(OH)2, from Oreana, Nevada
- Letter. Transformation of pentlandite to violarite under mild hydrothermal conditions
