Harrisonit, vzácný silikát-fosfát z granitických pegmatitů Českého masivuČlánek v PDF
Harrisonite, a rare silicate-phosphate from granitic pegmatites of the Bohemian Massif
Harrisonite, CaFe2+6(SiO4)2(PO4)2, is a rare silicate-phosphate described as a rock-forming mineral from highly metamorphosed garnetites (originally BIF) from Canada. Disregarding several questionable anthro pogenic occurrences of harrisonite, the mineral has also been scarcely found in the phosphatebearing granitic pegmatites Cyrilov (Czech Republic), Jocão (Brazil) and Přibyslavice (Czech Republic). The original harrisonite from garnetites is Mg-rich and Mn-poor, while that from pegmatites is enriched in Mn and poor in Mg. The average empirical formulae of harrisonite from Cyrilov and Přibyslavice based on 16 O are very similar, and are as follows: Ca0.98(Fe5.37Mn0.33Mg0.05Zn0.01)Σ5.76Si1.87P2.20O16, and Ca0.98(Fe5.37Mn0.33Mg0.06)Σ5.76Si1.89P2.19O16, respectively. Tetrahedrally coordinated Si in harrisonite from Přibyslavice and Cyrilov is often deficient and compensated by surplus of P. This surplus of P negatively correlates with the divalent cation contents, particularly Fe2+, which might indicate a participation of the MO6 polyhedron vacancies as a charge-balancing mechanism. The presence of harrisonite in phosphate-bearing granitic pegmatites is pointing out that the mineral is stable even at lower P–T conditions than reported from the type occurrence.
Jakub Vácha, Department of Geological Sciences, Masaryk University, Brno, Kotlářská 2, 611 37 Brno, Czech Republic and Czech Geological Survey, Leitnerova 22, 659 37 Brno, Czech Republic, e-mail: email@example.com
Radek Škoda, Department of Geological Sciences, Masaryk University, Brno, Kotlářská 2, 611 37 Brno, Czech Republic