Zincowoodwardite, [Zn1-xAlx(OH)(2)][(SO4)(X/2) (H2O)(n)], a new mineral ofthe hydrotalcite group

The new mineral zincowoodwardite has been found in the mining district Laur ion (Lavrion), Greece. It forms pale blue to bluish-white crusts of small p laty crystals measuring 5-10 mum across. The crystals usually have a hexago nal outline. The mineral has a white to bluish-white streak, a waxy lustre and a Mohs hardness of 1. The ideal chemical composition is [Zn1-XAlX(OH)(2 )] [(SO4)(X/2)(H2O)(n)] With X<0.67. A range of X = 0.32-0.50 was observed in natural and synthetic zincowoodwardite samples. Two different trigonal p olytypes were found, a 3R polytype (space group probably R<(3)over bar>m) w ith a = 3.065(1), c = 25.42(2)Angstrom, V = 206.8(2) Angstrom (3), Z = 3, a nd a 1T polytype (space group probably P (3) over bar) with a = 3.063(2), c = 8.91(1) Angstrom, V = 72.4 Angstrom (3), Z = 1. Measured density for the 3R polytype is 2.66 g/cm(3), the calculated density is 2.71g/cm(3). Zincow oodwardite is the zinc analogue of woodwardite and a lower hydrated analogu e of glaucocerinite. As with all members of the hydrotalcite group, zincowo odwardite has a hybrid layer structure of brucite-like (Me2+,Me3+)(OH)(2)-l ayers and anion-water-interlayers.