Naslov
First Occurrence of Dumortierite in Croatia : a Potential Evidence of Tetrahedral Ti Substitution for Si

Autori
Garašić, Vesnica ; Lugović, Boško ; Sekušak, Mirjana, Meyer, Hans-Peter ; Vrkljan, Maja ; Schuster, Ralf

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Goldschmidt Conference 2013 : abstracts ; u: Mineralogical magazine 77 (2013) (5) 1125-1238 / - Bratislava : Trnava, 2013, 1141-1141

Skup
Goldschmidt Conference 2013

Mjesto i datum
, 2013

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
dumortierite; tetrahedral substitution

Sažetak
Dumortierite (Al, □)Al6(BO3)Si3O13(O, OH)2 occurs in a pegmatite vein cutting S-type granite in the Late Cretaceous magmatic-metamorphic complex of Mt. Moslavačka gora, in the SW part of the Pannonian Basin, Croatia. The granitoid pluton intruded Abukuma type series of metamorphic rocks associated with migmatites. Dumortierite-bearing vein, up to 6 cm thick, consists of coarse-grained quartz, orthoclase, microcline and albite, less abundant muscovite, biotite, pinkish andalusite and blue-coloured dumortierite. The microscopic studies identified two types of dumortierite crystals: Dum I and Dum II. The Dum I crystals are subhedral prismatic up to 16 mm in size, strongly pleochroic ranging from colourless to azure blue. The Dum II type represents bundles of parallel fibrous or acicular crystals, up to 1, 4 mm long, strongly pleochroic from colourless to red violet. The Dum I crystals have lower contents of Mg (0.033-0.055 pfu) and Ti (0.001-0.011 pfu) than Dum II crystals (0.047-0.087 pfu and 0.043-0.064 pfu, respectively) whilst differences in Fe abundance (0.038-0.072 pfu vs. 0.037-0.057 pfu) and Al/Si ratios (2.35-2.47 vs. 2.27-2.49) are not significant. A Si deficiency (< of 3.0 pfu) is found in 95% of EPMA spot analysis of the dumortierite. The Si tetrahedral deficiency has been conventionally balanced by Al. A moderate correlation between 3-Si and Al (r = 0.606), and between 3-Si and Ti (r = 0.609) exists in the analysed dumortierites. Strong correlation between 3-Si and Al+Ti (r = 0.968) suggests that Ti in dumortierite replaces not only Al in octahedra as generally accepted, but also may substitute Si in tetrahedra.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

Napomena
Doi:10.1180/minmag.2013.077.5.7

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