The Borate Minerals are
minerals which contain a
borateanion 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.[2] The [B(O,OH)4− anion exists as well.
Many borate minerals, such as
borax,
colemanite, and
ulexite, are
salts: soft, readily soluble, and found in
evaporite contexts. However, some, such as
boracite, are hard and resistant to weathering, more similar to the
silicates.
There are over 100 different borate minerals.[2][3] Borate minerals include:
IMA-CNMNC proposes a new hierarchical scheme (Mills et al., 2009). This list uses it to modify the
Classification of Nickel–Strunz (
mindat.org, 10 ed, pending publication). Note that although Nickel–Strunz division letters were traditionally based on the number of boron atoms in a mineral's chemical formula (06.A are monoborates, 06.B are diborates, etc.), the IMA has reclassified borate minerals based on the polymerisation of the borate anion.
Abbreviations
REE:
rare-earth element (Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu)