Acta Musei Moraviae

Vivianite from the Quaternary sediments in Dolní Lutyně (Silesia, Czech Republic)

Vivianite was found in an active sand and gravel pit Dolní Lutyně – Velké Lány, Silesia, Czech Republic. It extracts mineral raw material from Quaternary fluvial? channels filled by glacifluvial gravel and sand with clayey intercalations of moraine origin, overlaid by melting water subglacial sediments of the progressive phase of glaciation and discontinuous sediments from the retreat glaciation phase. Loess loamy clays, peat clays, and peat are locally situated in their overburden. Vivianite forms powdery dark blue aggregates in the silt sediments with organic matter. The unit-cell parameters refined from X-ray powder diffraction data are: a = 10.0319(4), b = 13.4177(4), c = 4.6918(2) Å, β = 102.294(3)° and V = 617.06 ų. Microchemical analysis of vivianite (average from 6 spots) corresponds to the empirical formula Fe²⁺_2.99Mn²⁺_0.02Ca_0.01Mg_0.01(PO₄)_1.97 . 8.01 H₂O, as the water was calculated from the M²⁺ / H₂O ratio according to the ideal formula and after recalculation based on 16 oxygen atoms per formula unit. Minor isomorphic admixtures are Mn (max. 0.025 apfu), Mg (max. 0.020 apfu), and Ca (max. 0.015 apfu). Average SiO₂ content 0.57 wt. % might be ascribed to the surrounding clay matrix. Vivianite is associated with organic matter (leaves, seeds) deposited in the fluvial silt sediments, which supplied both P and reductive environment necessary for the mineral formation.