Ferrarisit z dolu Barbora v jáchymovském rudním revíru (Česká republika)

Very rare hydrated calcium arsenate, mineral ferrarisite, was found in the area of corridor 30-32 (vein No. 32, III. level of the shaft Barbora) of the Jáchymov ore district, Krušné hory Mountains, Czech Republic. Ferrarisite occurs as colourless to greyish white crystalline aggregates up to 5 mm in size or crystalline aggregates formed by parallel arranged acicular crystals up to 1 mm in length. Associated minerals are annabergite, picropharmacolite, pharmacolite, rauenthalite and guérinite. Ferrarisite is triclinic, space group P-1, the unit-cell parameters refined from X-ray powder diffraction data are: a 8.3000(10), b 6.7309(8), c 11.2129(12) Å, α 106.198(8)°, β 92.857(10)°, γ 99.183(9)° and V 590.90(12) Å3. Chemical analyses of ferrarisite correspond to the empirical formula Ca4.99(AsO4)1.93(PO4)0.06(AsO3OH)2.01·9H2O on the basis of As+P = 4 apfu. The origin of ferrarisite is interpreted as product of (sub)recent supergene alteration of primary arsenides in calcite gangue in environment of abandoned mine corridors.