Abstract
Two new mineral species, carraraite and zaccagnaite, were found in cavities in calcite veins in marble quarries of the Carrara basin (Apuan Alps, Italy). Carraraite, Ca3Ge(OH)6(SO4)1.08 (CO3)0.92 · 12H2O, occurs as submillimetric crystals, tabular on {001}. The cell dimensions are a = 11.056 (3), c = 10.629 (6) Å, and the space group is P63/m. Carraraite is optically uniaxial (–), ω = 1.509, ε = 1.479. The strongest lines of the X-ray diffraction pattern are at d-spacings (Å): 9.57 (vs) (100), 5.53 (s) (110), 3.83 (s) (112), 3.56 (ms) (202), 2.74 (ms) (302). Carraraite is a new member of the ettringite-thaumasite group, which is characterized by columns of composition [Ca3Ge(OH)6 ·12H2O]4+ running along c and interconnected through hydrogen bonding to (SO4)2− and (CO3)2− groups.
Zaccagnaite, Zn4Al2(OH)12(CO3) ·3H2O, occurs as minute hexagonal crystals, elongated parallel to [001]. The cell dimensions are a = 3.0725 (3), c = 15.114 (4) Å and the space group is P63/mmc. The crystals are always covered by a thin crust of fraipontite. The strongest lines of the X-ray diffraction pattern are at d-spacings (Å): 7.51 (vs) (002), 3.794 (m) (004), 1.542 (ms) (108), 1.539 (ms) (110). Zaccagnaite is a new member of the hydrotalcite-manasseite family; its structure is characterized by a regular alternation of brucite-like layers with composition (Zn2/3Al1/3)(OH)2 and an interlayer composed of carbonate groups and water molecules.
