Abstract: A composition which can be fiberized 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:______________________________________ SiO.sub.2 51-68 wt % Al.sub.2 O.sub.3 5-18 wt % ______________________________________with the total amount of SiO.sub.2 +Al.sub.2 O.sub.3 being from 62 to 75 wt %, ______________________________________ Na.sub.2 O 0-6 wt % K.sub.2 O 0-5 wt % ______________________________________with the total amount of Na.sub.2 O+K.sub.2 O being from 0 to 7.