Tourmaline of the elbaite-dravite series from an elbaite-subtype pegmatite at Bližná, southern Bohemia, Czech Republic
Novák, Milan; Selway, Julie B.; Černý, Petr; Hawthorne, Frank C.; Ottolini, Luisa
European Journal of Mineralogy Volume 11 Number 3 (1999), p. 557 - 568
published: May 25, 1999
manuscript accepted: Jan 6, 1999
manuscript received: Jun 2, 1998
ArtNo. ESP147051103014, Price: 29.00 €
Abstract The elbaite-subtype pegmatite at Bližná, near Černá v Pošumaví in southern Bohemia, Czech Republic, intrudes dolomite-calcite marble. It can be divided into two distinct units, unit A and unit B, and has a narrow exocontact zone along the edge of the pegmatite. The crystallization sequence of tourmaline from unit A is Ca-rich schorl-elbaite → Ca-rich elbaite-schorl-dravite → Mn-rich elbaite → Mn-rich liddicoatite → liddicoatite-elbaite, typical of tourmaline from elbaite-subtype pegmatites. The crystallization sequence of tourmaline from unit B is Na-rich uvite -> Ca-rich schorl-elbaite-dravite -»Ca-rich Mg-bearing elbaite → (Ca, Mn)-rich elbaite → Mn-rich liddicoatite-elbaite → Na-rich liddicoatite. Tourmaline from the exocontact ranges from Na-rich uvite → Ca-rich dravite -4 dravite-elbaite → Ca-rich Mg-bearing elbaite → liddicoatite-elbaite. The intermediate elbaite-schorl-dravite from unit A and schorl-elbaite-dravite from unit B are characterized by low F, moderate Mn and high Ti and Ca contents. The Mg-bearing elbaite from unit B and the exocontact is characterized by low Fe, moderate Ti, and high Ca and F contents. The dravite-elbaite from the exocontact is characterized by low Fe, Mn, Ti, Ca and F contents. The intermediate elbaite-schorl-dravite and elbaite-dravite solid-solutions crystallized as a result of mixing of (Ca, Mg)-rich fluids from the dolomite-calcite marble host-rock and exsolved (Na, Al, Li, F, B)-rich pegmatitic fluids. The factors controlling formation of elbaitedravite in rocks may be summarized as follows: high activities of Li, Mg, Al and B, high Li/Mg ratio in the parent medium, acidic conditions with pH < ~ 6, and lack of holmquistite. Consequently, elbaite-dravite solid-solutions should occur in highly contaminated elbaite-subtype pegmatites penetrating marble and in holmquistite-free contact aureoles around complex LCT pegmatites.