New data on balangeroite and carlosturanite from Alpine serpentinites

Systematic sampling of the serpentinites occurring in the Italian Western Alps has led to the discovery of several new localities where the fibrous silicates balangeroite (two sites) and carlosturanite (twenty-one sites) are abundantly present. While balangeroite is confined to the Lanzo Massif, carlosturanite is present in all fractured serpentinites of the explored area; it is absent in the foliated serpentinites. Correlations between the analysed cations show that minor elements represent structural substitutions, except for traces of Na and K which are due to impurities. Intergrowths of fibrous phases (in particular carlosturanite) with chrysotile, diopside, antigorite and olivine, are shown to be oriented associations. The refinement of a neutrondiffraction powder pattern of balangeroite allows the derivation of precise parameters for a monoclinic cell [a = 19.163(2), b = 19.224(2), c = 9.599(3) A, gamma = 89.50(1) degrees ]