Borate minerals
![Large (up to 1.8 cm) yellow londonite crystals associated with rubellite tourmaline. Londonite is an unusual caesium-rich heptaborate.[1]](/Images/godic/202502/07/Londonite-Tourmaline-1209773152.jpg")
The borate minerals are minerals which contain a borate anion group. The borate (BO3) units may be polymerised similar to the SiO4 unit of the silicate mineral class. This results in B2O5, B3O6, B2O4 anions as well as more complex structures which include hydroxide or halogen anions. The [B(O,OH)4] anion exists too.