Studium nově zjištěných fosfátů z opuštěného lomu Třenice u Zbiroha (Česká republika)

A study of phosphate mineralization from the abandoned Třenice quarry near Zbiroh (Beroun district, Czech Republic) provides analytical data for newly determined minerals beraunite, crandallite and natrodufrénite. Phosphate minerals are bound to cracks and cavities in Ordovician greywackes and silicites or quartz sandstones of the Barrandian area. Beraunite occurs as rusty red flat elongated crystals up to 7 mm in size, often forming radial aggregates; its empirical formula is (Fe3+5.05Al0.77Ca0.01)Σ5.83[(PO4)3.99(SiO4)0.01]Σ4.00O(OH)3.55·6H2O. It is monoclinic, space group C2/c with refined unit-cell parameters: a 20.643(4), b 5.1436(13), c 19.243(3) Å, β 93.56(5)° and V 2039.3(7) Å3. Natrodufrénite forms light to dark green spherical aggregates reaching 0.5 - 1.5 mm in size; its empirical formula is (Na0.33Ca0.13□0.54)Σ1.00(Fe2+0.81Mg0.01)Σ0.82(Fe3+4.47Al0.53)Σ5.00(PO4)4.00(OH)5.21·2H2O. It is monoclinic, space group C2/c, with refined unit-cell parameters: a 25.841(8), b 5.152(3), c 13.776(6) Å, β 111.5(4)° and V 1704.8(5) Å3. Crandallite forms light beige powdery layers in a mixture with wavellite. Its empirical formula is (Ca0.79Ba0.11Sr0.11)Σ1.01(Al2.96Fe3+0.02)Σ2.98[(PO4)0.91(SO4)0.09]Σ1.00(PO3OH)1.00(OH)7.06. The mineral is trigonal, space group R-3m with refined unit-cell parameters: a 7.001(3), c 16.1903(8) Å and V 687.0(5) Å3.