An investigation of matrix effects in the analysis of fluorine in humite-group minerals by EMPA, SIMS, and SREF

Abstract

Accurate determination of F in minerals is a diffi cult task even when high F concentrations are present. Fluorine usually is determined by means of electron micro-probe analysis (EMPA) standardized on non-silicate-matrix compounds (e.g., fl uorite), and some previous work has revealed the diffi culties in determining F at high concentrations such as found in the humite-group minerals. Moreover, when both single-crystal structure refi nement (SREF) and EMPA are available for the same crystal, the two estimates do not always agree. On the other hand, the secondary ion mass spectrometry (SIMS) technique is not easily applied at high F concentrations due to the existence of matrix effects related to the chemical composition and structure of the sample as well as to the concentration of the element itself. We tested the agreement among these analytical techniques in the estimation of high F contents and propose an analytical procedure for the analysis of fl uorine. Our results indicate that careful selection of working conditions for EMPA of F together with appropriate correction, can yield accurate fl uorine concentrations in minerals. Fluorine data extracted from refi ned site occupancies are systematically overestimated. New accurate working curves have been worked out for SIMS analysis of F taking Si and Mg, in turn, as the reference element for the matrix. Humite-group minerals show SIMS matrix effects on the order of ~10%. In analyzing fl uoborite in the most unfavorable cases, the difference in Ion Yield (F/Mg) between "disoriented" humite-group minerals and "oriented" fl uoborite samples can reach ~27%. Finally, a lower than expected IY(F/Si) from the F/Si working curve (made with humite minerals) is shown by topaz, which can be ascribed to chemical matrix effects, as well as to the covalent-type bonding between F and the major element in the matrix (Al). they possess lower resolving power than TAP (Fialin et al. 1993). With these new refl ectors, multiple-order interferences greater than the second-order are absent (e.g., the third-order PKα peak in apatite). Nevertheless, interferences due to second-order peaks from Mg and Al and fi rst-order L-lines from Fe still survive and constitute a limitation in the determination of fl uorine in minerals rich in Mg, Al, and transition elements (Raudsepp 1995).

Hydration effects on crystal structures and equations of state for silicate minerals in the subducting slabs and mantle transition zone

“…Gibbs et al, 1970;Robinson et al, 1973;Yamamoto, 1977;Fujino and Takuchi, 1978;Ottolini et al, 2000;James, 2001, 2002;Friedrich et al, 2001Friedrich et al, , 2002Kuribayashi et al, 2004;Kunz et al, 2006;Ye et al, 2013Ye et al, , 2015. Natural chondrodite and clinohumite samples have been found in metamorphosed limestones and dolomites (Friedrich et al, 2002), as well as in serpentinized wehrlite .…”

“…Norbergite: Gibbs and Ribbe (1969); humite: Ribbe and Gibbs (1971); Chondrodite: Gibbs et al (1970), Yamamoto (1977), Fujino and Takuchi (1978), Ottolini et al (2000), Friedrich et al (2001Friedrich et al ( , 2002; Berry and James (2002) …”

“…,Kuribayashi et al (2004),Kunz et al (2006),Ye et al (2015); clinohumite:Robinson et al (1973);Fujino and Takuchi (1978),Ottolini et al (2000), James (2001), Friedrich et al (2001),Ye et al (2013).…”

FTIR and Raman spectroscopy characterization of fluorine-bearing titanian clinohumite in antigorite serpentinite and chlorite harzburgite

“…Fluorine abundance in solid materials can often be measured using an electron microprobe, as in the case of the large TiChu crystals in this study, but accurate F measurements by an electron microprobe are not routine and require some developments (Ottolini et al 2000). Estimation of the chemical composition from IR spectra is probably a useful alternative for cases such as complex intergrowths of TiChu with olivine.…”

Hydrogen distribution in chondrodite: a first–principles calculation

“…If H1 site is fully (100%) occupied by hydrogen, short H1-H1 distance is resulted in the structure, and it is generally thought that such configuration is less favored. On the other hand, in natural humite group minerals including chondrodite containing F/(F + OH) > 0.5, hydrogen occupying only at H1 site has been reported (e.g., Ottolini et al, 2000). For Ticontaining chondrodite and clinohumite, again hydrogen occupying only at H1 site was observed (Fujino and Také-uchi, 1978).…”