Balangeroite, a new fibrous silicate related to gageite from Balangero, Italy

Balangeroite occurs as brown asbestiform fibers in a paragenesis with long-fiber chrysotile, magnetite, and native Fe-Ni in the Balangero serpentinite (Lanzo Valley, Piedmont, Italy). It is orthorhombic with a 13.85(4), b 13.58(3), and c 9.65(3)Å; a sub-cell with c' = c/3 is strongly evident. The X-ray powder pattern demonstrates an isostructural relationship of the new mineral with gageite; the strongest reflections are: 9.59(40)(110), 6.77(80)(020), 3.378(45X410), 3.278(40)(140), 2.714(100)(050,510), 2.674(75)(150,223), and 2.516(40)(250). The fibers are elongated parallel to [001], show one or more {hk0} cleavages, and are usually intergrown with chrysotile. The refractive indexes are about the same, 1.680(5), both parallel and perpendicular to [001]; color is dark brown and yellow brown in these two directions, respectively. Chemical analysis gives a unit-cell content of and the presence of a sub-cell with c' = c/3 suggests the formula with contents divisible by 3; a similar formula is probably also correct for the Mn-analogue, gageite. DTA, TGA, and high-temperature X-ray powder analyses show structural breakdown with a total weight loss of 9.4% and the appearance of olivine at 800°C. The infrared spectrum shows strong absorptions corresponding to vibrations in OH^- and (Si0₄)^4- groups.