A borate is any salt of boric acid (H3BO3) or of more complex oxyacids of boron. Many borates exist as minerals, the most important of which are borax, colemanite, and kernite – all used as sources of boron compounds. Borates readily form glasses. H2O2 (hydrogen peroxide) or Na2O2 give peroxyborates used in washing powders.


Borates contain planar trigonal BO3 and tetrahedral BO4 groups, either of which may be discrete or linked. Hydroxyl groups may be coordinated to boron. Pyroborates, e.g., Co2B2O3, contain two BO3 linked through one oxygen. Polyborates contain infinite chains or rings, e.g. B3O3 rings in metaborates (B3O6)3- or linear [BO2]nn- (in LiBO2), two rings linked through a tetrahedral boron KB5O6(OH)4.2H2O.


Borate esters (B(OH)3 plus ROH plus H2SO4) are known for most alcohols; anionic derivatives, e.g. Na(BH(OR)3) are formed and acyl borates B(O2CR)3 are also known. (HO)2.B(OH)2 forms esters.