Hydrowoodwardite, a new mineral of the hydrotalcite group from Konigswaldenear Annaberg, Saxony/Germany and other localities

The new mineral hydrowoodwardite has been found at the St. Briccius mine, K onigswalde near Annaberg, Saxony, Germany and other localities. Hydrowoodwa rdite is a higher hydrated analogue of woodwardite, the Cu-analogue of glau cocerinite and carrboydite and a member of the hydrotalcite group. The chem ical composition is [Cu1-xAlx(OH)(2)] [(SO4)(x/2) (H2O)(n)] with x < 0.67 a nd n > approximate to 3x/2. A range of x = 0.23-0.62 was observed in natura l and synthetic hydrowoodwardite samples. The mineral forms blue botryoidal porous crusts. Hydrowoodwardite is trigonal (space group probably <R(3)ove r bar>m), with unit cell parameters a = 3.070(7), c = 31.9(2) Angstrom, V = 260(2) Angstrom(3), Z = 3. Measured density is 2.33 g/cm(3), calculated de nsity is 2.48 g/cm(3). As with all members of the hydrotalcite group, hydro woodwardite has a hybrid layer structure of brucite-like (M2+,M3+) (OH)(2)- layers and anion-water-interlayers.