a class of minerals, salts of boric acids. They include orthoborates, metaborates, tetraborates, and salts of polyboric acids. The bases of the structure of natural borates are boric oxygen triangles [BO3]3– and tetrahedrons (BO4)5– with possible substitution of part of the O by OH1– or combinations thereof. Analogously to silicic oxygen tetrahedrons of silicates, the boric oxygen triangles and tetrahedrons, when combining, may form chain, strip, stratified, or shell structures. There are anhydrous and hydrous borates, the latter being more common. Most borates are white or colorless; they are crystallized predominantly into rhombic and monocline systems.
Natural borate deposits arise in different ways. The largest of them (storing tens and hundreds of millions of tons of B2O3) are vulcanogenic-sedimentary deposits. Endogenetic deposits (storing up to tens of millions of tons of B2O3) are associated almost exclusively with skarns. Halogenic-sedimentary deposits (containing several millions of tons of B2O3) occur jointly with the salt deposits of dried-up marine basins.
The main industrial minerals from vulcanogenic-sedimentary deposits are sodium, calcium, and calcium-sodium hydrous borates:
ulexite NaCa [B5O6(OH)6] · 5H2O
kernite and borax Na2[B4O6(OH)2] · 3H2O
and Na2 [B4O5(OH)4] · 8H2O
colemanite Ca [B3O4(OH)3] · H2O
inyoite Ca [B3O3(OH)5] · 4H2O
priceite 5CaO · 6B2O3 · 9H2O
In halogenic-sedimentary deposits, calcium, calcium-sodium, and magnesium hydrous borates predominate, including ulexite, colemanite, inyoite, inderite Mg[B3O3(OH)5]5H2O, szaibelyite Mg2[B2O4(OH)] (OH), and hydroboracite CaMg[B3O4(OH)3]23H2O. Boracite is found in some deposits.
The main industrial minerals of skarn deposits are basically anhydrous magnesium and magnesium-ferrous borates: suanite Mg2[B2O5], cotoite Mg3[BO3]2, minerals of the lud-wigite group
(Mg, Fe2+)2 (Fe3+, Al, Sn4+) [BO3] O2
and lower temperature szaibelyites, developing with substitution of other borates.
The most important deposits of the vulcanogenic-sedimentary type are found in the USA (California and neighboring states), and in Peru, Chile, Argentina, Turkey, and China (Tibet).
Endogenetic deposits are found in the Soviet Union (Western and Eastern Siberia, the Far East, Kazakhstan, and Middle Asia), China (northeastern provinces), North Korea, and Rumania.
Industrial deposits of halogenic-sedimentary type are known only in Kazakhstan (at Inderskoe and elsewhere).
REFERENCESBerlin, L. E., and N. N. Pertsev. Bor, 2nd ed. (Trebovaniia pro-myshlennosti k kachestvu mineral nogo syr’ia, vol. 69.) Moscow, 1961.
Iarzhemskii, Ia. Ia. Voprosy formirovaniia boratov. Moscow, 1968.
N. N. PERTSEV