Abstract: Asbestos cement may be converted to a harmless product by melting at a melt temperature of 1400.degree. to 1700.degree. C. a blend of 50 to 85% by weight asbestos cement with 15 to 50% by weight of additives that include naturally occurring silicate material such that the total blend has a CaO content of not more than 50%. The melt is discharged from the furnace, cooled and solidified and may be used as aggregate or, generally after solidification as regular units, may be used as part or all of the charge for producing MMV fibre material. It is of particular value for the production of man made vitreous fibre material that has low alumina content and is soluble in lung fluids.

Abstract: A fiberizable mineral composition which is thermostable and has a high dissolution rate in biological fluids includes 53.5-64 w/w % of SiO.sub.2, up to 4 w/w % of Al.sub.2 O.sub.3, 10-20 w/w % of CaO, 10-20 w/w % of MgO, and 6.5-9 w/w % of FeO, the total amount of FeO and Fe.sub.2 O.sub.3 calculated as FeO. A mineral fiber material made from the composition can be used for thermal and/or acoustic insulation purposes or as a plant growing medium or substrate.