Titanium in tourmalines from granitic pegmatites and their exocontacts

Dutrowite, Na(Fe2+2.5Ti0.5)Al6(Si6O18)(BO3)3(OH)3O, a new mineral from the Apuan Alps (Tuscany, Italy): the first member of the tourmaline supergroup with Ti as a species-forming chemical constituent

“…2a, b), vibrational modes of Y O 6 (in the range ∼ 200-240 cm −1 ), ZO 6 (range 360-375 cm −1 ), SiO 4 rings vibrations (between ∼ 650 and 720 cm −1 ), BO 3 bending and stretching modes (in the range 730-780 cm −1 ), and SiO 4 stretching modes (between 760 and 1120 cm −1 ) occur, in agreement with previous authors (e.g. Gasharova et al, 1997;Watenphul et al, 2016a, b). The stretching of O-H bonds occurs in the region between 3400 and 3800 cm −1 (Fig.…”

“…The possible involvement of Ca 2+ in the substitution favouring the incorporation of Ti in the crystal structure of tourmaline, suggested by some authors (e.g. Dini et al, 2008;Gadas et al, 2019), is not supported by the current data; indeed, chemical data are quite scattered, and Ca enrichment in dutrowite with respect to oxy-dravite (∼ 0.06 apfu) is low. Consequently, chemical data collected on type material of dutrowite are consistent with previous studies on both natural (e.g.…”

“…Some previous data also indicated a decrease in the OH content and an increase in the oxy-nature of tourmalines (e.g. Gadas et al, 2019), coupled with the Ti incorporation via the substitution Al 3+ + (OH) − = Ti 4+ + O 2− . Such a mechanism may also occur in dutrowite, possibly coupled with the other involving Mg and Fe, e.g.…”

“…Grice and Ercit (1993) reported data for two tourmalines having 2.87 wt % and 2.19 wt % TiO 2 ; these values correspond to 0.40 and 0.29 Ti apfu, respectively. Still higher TiO 2 contents, 4.70 wt %, were later measured in a bosiitelike tourmaline by Flégr et al (2016); this weight percent Titanium-rich tourmaline supergroup minerals have been identified in the Třebíč pegmatites, Manjaka and Řečice, in the Czech Republic, with Ti contents up to 0.55, 0.59, and 0.64 apfu, respectively (Novák et al, 2011;Gadas et al, 2019). Konzett et al (2012) measured up to 3.42 wt % TiO 2 in tourmaline from (Fe,Ti)-rich eclogite from the Kreuzeck Mountains, Eastern Alps, Austria.…”

“…Watenphul et al (2016a, b) discussed the relations between band positions and crystal chemistry of the studied tourmalines. In particular, the vibrational modes of Y O 6 and ZO 6 polyhedra are sensitive to the Mg contents and Fe contents, as well as to the Fe oxidation state (Watenphul et al, 2016b); similarly, the short-range cation distribution around the O(1) and O(3) sites affects the band positions in the O-H stretching region (Gonzalez-Carreño et al, 1988;Bosi et al, 2015;Watenphul et al, 2016a). Specifically, the band at about 3565 cm −1 is related to O(3), whereas the less-intense band at about 3636 cm −1 is related to O(1).…”