Serpentinites: from dimension stones to valuable industrial minerals

Serpentinites are used as dimension stones, commercialized as “green marbles” with many different textures and color shades: an excellent example is represented by the Valmalenco area (central Alps, northern Italy). There are two main commercial varieties, depending on texture and microstructures: “schistose” (splitted in thin slabs) and “massive” (polished, sandblasted, etc.). The main rock-forming minerals are represented by antigorite (60 – 90 wt.%) and olivine (up to 30 wt.%), with smaller amounts of clinopyroxene (diopside), chlorite and magnetite. The very fine grain size and the interpenetrated microstructure confer these materials excellent technical properties (compressive and flexural strength, freeze-thaw resistance). The quarrying and processing waste can be estimated around the 40 - 50 % of the extracted material, and at present time there are no virtuous reuses of the waste materials. However, considering the peculiar chemical and mineralogical composition of serpentinitic rocks, there are many possibilities of reuse in the industrial mineral sector. Finely ground antigorite-rich materials could be used as filler for plastics and rubber (instead of talc), whereas olivine-rich wastes as a reactive fixing carbon dioxide (as carbonates, i.e. magnesite) released during the use of fossil fuels. Recently, research has been funded aimed at serpentine carbonation using microwaves, in order to optimize the process and reduce as much as possible energy consumption. In the ceramic industry, the most promising target is represented by forsterite and/or high-MgO ceramics and forsterite refractories (with periclase addition), but also by cordierite ceramics (adding kaolin) and high-hardness vitroceramics. The real possibility of an industrial use of serpentinitic materials will require much more experimental work, because no relevant previous studies are available. Special care must be taken to avoid chrysotile asbestos contamination, which can be occasionally dispersed in the rock mass.