The present invention relates to boron-containing compositions. The invention relates to comminuted, heterogeneous boron-containing compositions which are obtainable by a process which comprises heating to a temperature sufficiently high that calcination occurs but insufficient for the formation of a homogeneous melt a mixture comprising components capable, under the conditions of heating, of forming the oxides B2O3 and SiO2 and optionally Al2O3, Na2O and/or CaO in proportions such that the relative percentages by weight of the said oxides, based on the total weight of said oxides, are as follows: 5 to 35% B2O3； 10 to 65% SiO2； 0 to 35% Al2O3； and up to 20% Na2O and/or up to 50% CaO； with the proviso that the said B2O3 content is not 10 to 18%, when the other contents are as follows: 40 to 65% SiO2, 17 to 32% Al2O3 4 to 9% Na2O, and 0 to 10% CaO, and then comminuting the resulting composition. By varying the proportions of the ingredients and the heating conditions, there may be obtained products of differing boron solubility characteristics according to the desired use of the products. Such compositions may be used as a source of boron in ceramics and heavy clay bodies, glass and fiberglass； in agriculture； as wood preservatives and pesticides； in polymers and rubbers； in wood, including wood-plastic composites； as flame retardant； in intumescent materials； in paints and coatings, in soaps and detergents； in cosmetics； in industrial fluids； in steel slag； in water treatment； and in gypsum wallboard as well as in glazes.
