Inclusive chemical characterization of tourmaline; Mossbauer study of Fe valence and site occupancy

Dyar, M. D.; Taylor, Marjorie E.; Lutz, Tim; Francis, Carl A.; Guidotti, Charles V.; Wise, Michael A.

doi:10.2138/am-1998-7-817

Cited by 139 publications

(93 citation statements)

References 29 publications

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“…However, there is no correlation between Si and B to suggest that the "excess" boron occupies tetrahedral sites and in fact, some of the samples with "excess" B also have greater than the stoichiometric 6 Si cations pfu. Without crystallographic study of the samples we cannot rule out or confirm the presence of tetrahedral boron but we consider it likely that much of excess B results from accumulated analytical errors propagated in the mineral formula calculations, as mentioned by Dyar et al (1998).…”

Section: General Observationsmentioning

confidence: 97%

“…A single analysis consisted of 50 scans of the peak stepping sequence 0.95 background (0.1 s), 10 B (4 s) and 11 B (2 s) resulting in a total analysis time of 11 minutes including preburn. The combined instrumental and matrix-induced isotopic fractionation was calibrated using tourmaline reference dravite (Harvard mineral collection #108796), schorl (#112566) and elbaite (#98144) described by Dyar et al (1998;. Instrumental mass fractionation (IMF) was monitored by 3-5 daily measurements on each of the reference tourmalines during the analytical session.…”

Section: Geologic Settingmentioning

confidence: 99%

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Chemical and boron-isotope variations in tourmalines from an S-type granite and its source rocks: the Erongo granite and tourmalinites in the Damara Belt, Namibia

Trumbull

Krienitz

Gottesmann

et al. 2007

Contrib Mineral Petrol

124

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Tourmaline is widespread in metapelites and pegmatites from the Neoproterozoic Damara Belt, which form the basement and potential source rocks of the Cretaceous Erongo granite. This study traces the B-isotope variations in tourmalines from the basement, from the Erongo granite and from its hydrothermal stage. Tourmalines from the basement are alkali-deficient schorl-dravites, with Bisotope ratios typical for continental crust (δ 11 B average -8.4‰ ±1.4, n=11; one sample at -13‰, n=2).Virtually all tourmaline in the Erongo granite occurs in distinctive tourmaline-quartz orbicules. This "main-stage" tourmaline is alkali-deficient schorl (20-30% X-site vacancy, Fe/(Fe+Mg) 0.8 to 1), with uniform B-isotope compositions (δ 11 B -8.7‰ ±1.5, n=49) that are indistinguishable from the basement average, suggesting that boron was derived from anatexis of the local basement rocks with no significant shift in isotopic composition. Secondary, hydrothermal tourmaline in the granite has a bimodal B-isotope distribution with one peak at about -9‰, like the main-stage tourmaline and a second at -2‰. We propose that the tourmaline-rich orbicules formed late in the crystallization history from an immiscible Na-B-Fe-rich hydrous melt. The massive precipitation of orbicular tourmaline nearly exhausted the melt in boron and the shift of δ 11 B to -2‰ in secondary tourmaline can be explained by Rayleigh fractionation after about 90% B-depletion in the residual fluid.2

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Section: General Observationsmentioning

confidence: 97%

Section: Geologic Settingmentioning

confidence: 99%

Chemical and boron-isotope variations in tourmalines from an S-type granite and its source rocks: the Erongo granite and tourmalinites in the Damara Belt, Namibia

Trumbull

Krienitz

Gottesmann

et al. 2007

Contrib Mineral Petrol

124

View full text Add to dashboard Cite

show abstract

“…In the present case, there is even greater similarity in crystal structure between standards (dravite -schorl -elbaite solid solutions) and unknown (olenite). However, the standards contain far more Fe and Mn; these two ions constitute 4.7 to 12% of the total cations (Dyar et al 1998, sample nos. 1-3) versus 0.03% in the olenite.…”

Section: Chemical Analysismentioning

confidence: 99%

Tetrahedrally Coordinated Boron in a Tourmaline: Boron-Rich Olenite From Stoffhutte, Koralpe, Austria

Hughes¹,

Ertl²,

Dyar³

et al. 2000

The Canadian Mineralogist

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The substitution of [4] B for [4] Si in tourmaline has been the source of much discussion. A sample of olenite from Stoffhütte, Koralpe, Styria, Austria has been found to contain more than one [4] B per formula unit of 31 (O,OH,F), demonstrating that significant [4] B = [4] Si substitution does indeed occur in tourmaline. The composition of the structurally characterized crystal was determined using electron microprobe and SIMS data; in combination with refinement of the site scattering, the chemical data yield (3), c 7.0638(9) Å. The atomic arrangement was refined to R = 0.014 using X-ray data; is equal to 1.609 Å, reflecting substitution of the smaller boron atom for Si. Conjecture on the pattern of distribution of [4] B can be made on the basis of X-site occupancy.

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“…Nevertheless, an excess of boron over 3.0 atoms per formula unit (apfu) has been observed in compositions of some tourmaline crystals for which B 2 O 3 was determined directly (e.g. Barton 1969;Dyar et al 1994Dyar et al , 1998. Such elevated B content indicates that the B site is completely filled by the element, and the surplus has to enter another cationic lattice position.…”

Section: Introductionmentioning

confidence: 99%

Si-deficient foitite with [4]Al and [4]B from the ‘Ługi-1’ borehole, southwestern Poland

Pieczka¹,

Buniak²,

Majka³

et al. 2012

J. Geosci.

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A tourmaline depleted in Si has been found in the cement of Upper Rotliegend aeolian sandstone overlaying Lower Rotliegend volcanic rock in the 'Ługi-1' prospecting borehole near Jarocin in the Fore-Sudetic Monocline, south-western Poland. Tourmaline, representing Mg-bearing foitite, crystallized around quartz grains in the form of radial aggregates of tiny crystals, reaching only 1-2 μm in diameter. Due to the very small size of the tourmaline crystals and the presence of significant contents of transitional metals in the crystal lattice, only direct determination of B 2 O 3 in nm-sized spots enables evaluation of [4] Al and [4] B. Compositions of the tourmaline in successive analytical spots show that Si deficiency is supplemented both by [4] Al (0.00 to 0.48 Al apfu) as well as by [4] B (0.00 to 0.83 B apfu) at varying proportions. The origin of the mineral was related to diagenesis of evaporate sediments inducing reactions of quartz and clay minerals as primary components in the tourmaline-bearing sandstone with Ca saturated pore brines rich in Cl -and (BO 3 ) 3-.

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Inclusive chemical characterization of tourmaline; Mossbauer study of Fe valence and site occupancy

Cited by 139 publications

References 29 publications

Chemical and boron-isotope variations in tourmalines from an S-type granite and its source rocks: the Erongo granite and tourmalinites in the Damara Belt, Namibia

Chemical and boron-isotope variations in tourmalines from an S-type granite and its source rocks: the Erongo granite and tourmalinites in the Damara Belt, Namibia

Tetrahedrally Coordinated Boron in a Tourmaline: Boron-Rich Olenite From Stoffhutte, Koralpe, Austria

Si-deficient foitite with [4]Al and [4]B from the ‘Ługi-1’ borehole, southwestern Poland

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