Composition for high temp. fiberisation

A composition which can be fiberised to form high quality insulation wool, and which has been formulated from naturally-occuring rock minerals such as basalts, granites, limestone, dolomite and sandstone, optionally including by-products of industrial processes such as molybdenum or steel slag and grate ash, and/or high alumina materials such as China Clay and/or boron containing minerals such as Ulexite, said composition comprising the following components, given in wt%, based on the total weight of the composition: SiO2 51 - 68 wt%, Al2O3 5 - 18 wt%, with the total amount of SiO2 + Al2O3 being from 62 to 75 wt%, Na2O 0 - 6 wt%, K2O 0 - 5 wt%, with the total amount of Na2O + K2O being from 0 to 7.5 wt%, MgO 1 - 9 wt%, CaO 8 - 20 wt%, with the total amount of MgO + CaO being from 12 to 27 wt%, Fe2O3 2 - 10 wt%, TiO2 0 - 3 wt%, P2O5 less than 1 wt%, B2O3 0 - 3 wt%, the composition having a liquidus temperature of 1225 DEG C or less, and a viscosity at least 1000 poise at the liquidus temperature. These compositions are suitable for preparing insulation wool of high quality by a rotating internal centrifuging spinner fiberisation process.