Tourmaline of the elbaite-dravite series from an elbaite-subtype pegmatiteat Blizna, southern Bohemia, Czech Republic

The elbaite-subtype pegmatite at Blizna, near Cerna v Posumavi in southern Bohemia, Czech Republic, intrudes dolomite-calcite marble. It can be divide d into two distinct units, unit A and unit B, and has a narrow exocontact z one along the edge of the pegmatite. The crystallization sequence of tourma line from unit A is Ca-rich schorl-elbaite --> Ca-rich elbaite-schorl-dravi te --> Mn-rich elbaite --> Mn-rich liddicoatite --> liddicoatite-elbaite, t ypical of tourmaline from elbaite-subtype pegmatites. The crystallization s equence of tourmaline from unit B is Na-rich uvite --> Ca-rich schorl-elbai te-dravite --> Ca-rich Mg-bearing elbaite --> (Ca, Mn)-rich elbaite --> Mn- rich liddicoatite-elbaite --> Na-rich liddicoatite. Tourmaline from the exo contact ranges from Na-rich uvite --> Ca-rich dravite --> dravite-elbaite - -> Ca-rich Mg-bearing elbaite --> liddicoatite-elbaite. The intermediate el baite-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-be aring elbaite from unit B and the exocontact is characterized by low Fe, mo derate Ti, and high Ca and F contents. The dravite-elbaite from the exocont act 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 marbl e host-rock and exsolved (Na, Al, Li, F, B)-rich pegmatitic fluids. The fac tors controlling formation of elbaite-dravite in rocks may be summarized as follows: high activities of Li, Mg, Al and B, high Li/Mg ratio in the pare nt medium, acidic conditions with pH <similar to 6, and lack of holmquistit e. Consequently, elbaite-dravite solid-solutions should occur in highly con taminated elbaite-subtype pegmatites penetrating marble and in holmquistite -free contact aureoles around complex LCT pegmatites,