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.

Abstract: A low alkali borosilicate glass composition comprising60 to 78% by weight of SiO.sub.210 to 25% by weight of B.sub.2 O.sub.33.5 to 6.0% by weight of R.sub.2 O, wherein R.sub.2 O represents Na.sub.2 O, K.sub.2 O and/or Li.sub.2 O,2.0 to 6.5% by weight of CeO.sub.2, and0.25 to 8.0% by weight of Sb.sub.2 O.sub.3 and/or As.sub.2 O.sub.3,the percentages being based on the total weight of the glass composition. The glass composition of the invention are suitable for use as protective covers for solar cells, especially solar cells which are used in satellites.

Abstract: Alkali-resistant glass fibres for use as reinforcement in cementitious products are formed from a composition comprising, in weight percentages:______________________________________ SiO.sub.2 55 to 75% R.sub.2 O 11 to 23% ZrO.sub.2 6 to 22% Cr.sub.2 O.sub.3 0.1 to 1% Al.sub.2 O.sub.3 0.1 to 7% Rare earth oxides + TiO.sub.2 0.5 to 16% ______________________________________where R.sub.2 O is any one or more of Na.sub.2 O, K.sub.2 O or Li.sub.2 O, the content of TiO.sub.2 does not exceed 10%, and the total of the components recited above amounts to at least 88% by weight of the glass, the glass having been melted under non-oxidizing conditions such that all or a substantial proportion of the chromium in the glass is in the trivalent state.Cementitious products incorporating such fibres, e.g. in a proportion of 3 to 6 weight %, can be made using a Magnani-type asbestos cement machine or by a "spray-up" method.

Abstract: Alkali-resistant glass fibres, in the form of continuous-filament for use as reinforcement in cementitious products, or in the form of glass wool, are given enhanced alkali resistance by the incorporation of ThO.sub.2. The fibres are formed from a glass composition comprising, in weight percentages:______________________________________ SiO.sub.2 50 to 75% ThO.sub.2 + ZrO.sub.2 5 to 30% with ThO.sub.2 at least 0.4% R.sub.2 O 0 to 25% R'O 0 to 40% R.sub.2 O + R'O 10 to 40% Rare earth oxides 0 to 20% ______________________________________the content of ThO.sub.2 being at least 1% when the content of ZrO.sub.2 is less than 6% but not exceeding 9.5% when ZrO.sub.2 exceeds 8%, where R.sub.2 O represents Na.sub.2 O, K.sub.2 O or LiO.sub.2, with K.sub.2 O not exceeding 10% and Li.sub.2 O not exceeding 5% and R'O represents one or more of MgO, CaO, SrO, BaO, ZnO and MnO.