Greenstone is a recycled construction aggregate. Black slag arising from the Electric Arc Furnace process represents the core material of the aggregate. This residue is a ternary blend of oxides which is 100% inert thanks to a customized process patented in collaboration with Politecnico di Milano. Once produced and transformed, the black slag becomes Greenstone; the product has several granulometries certified via 2+ system and according to UNI EN 12620, 13043 and 13242.The aggregate is sold to external companies to be used in road pavements, cement aggregates and bituminous conglomerates. The adoption of the Greenstone aggregate allows to avoid the depletion of inert natural materials such as gravel, with savings in terms of land use.