Natural borates

NATURAL BORATES (EN: borates; DE: naturliche Borate; FR: borates naturels; ES: boratos naturales; RU: бораты природные) is the class of minerals, salts of boric acids, hydroxy-fluoroborates, and carbonatoborates. Among the natural borates proper, there have been identified the ortho-, meta-, pyroborates, and the salts of polyboric acids. They distinguish the anhydrous and more distributed hydrous natural borates. They crystallize themselves into rhombic, monoclinic, and, less often, into cubic or trigonal crystal systems. At the basis of the structures of natural borates, there are the isolated or joined [BO3]3- triangles, and [BO4]5- tetrahedra. According to analogy with silicates, they distinguish the island, chained, ribbon, layered, and framework natural borates.

Most natural borates are colourless or slightly coloured, with the exception of their magnesial-ferruginous varieties. Natural borates are polygenic minerals. The largest clusters of natural borates are situated within the volcanogenic-sedimentary (with the reserves of B2O3 of up to tens or hundreds of millions tonnes), endogenous contact-metasomatic (up to tens of millions tonnes), and halogen-sedimentary (up to several millions tonnes) deposits. Natural borates have been also noted within pegmatites (jeremejevite AlBO3). The main industrial minerals of the volcanogenic-sedimentary deposits are sodium, calcium, and calcium-sodium hydrous borates: ulexite, kernite Na2B4O7•4H2O, borax, colemanite, inyoite Ca2B6O11•13H2O, priceite Ca4B10O19•7H2O, and others. Within the halogen-sedimentary deposits, there are ulexite, colemanite, inyoite, hydrous magnesium borates: inderite Mg2B6O11•15H2O, ascharite, hydroboracite and boracite Mg3B7O13Cl. Within the contact-metasomatic deposits, there are magnesial, calcium-magnesial, and magnesial-ferruginous anhydrous borates: suanite Mg2B2O5, kurchatovite CaMgB2O5, kotoite Mg2[BO3]2, minerals of the ludwigite group and sakhaite Ca12Mg4[BO3]7(CO3)4(OH)2Cl•H2O; there is locally distributed fluoborite Mg3[BO3](F,OH)3. The largest volcanogenic-sedimentary deposits are known within the USA (California, Nevada states), Argentina, Chile and Peru, and also within Turkey and China; the contact-metasomatic deposits are known within the USSR, USA, Peru, China, North Korea, Romania, East Germany; the halogen-sedimentary deposits are known within the USSR and China.