Most of them
are rare, but
colemanite and ulexite are quite common and form large deposits.
Borax crystals. By Annouk via Flickr.com
Borax is a
sodium borate hydrate. It forms tabular or prismatic
crystals, but can also be massive in habit. It is most often white but
can also be colourless, grey, blueish or greenish. It is an evaporative
mineral and forms in evaporative deposits in desert lakes that dry out.
It can also be found in hot springs.
Colemanite, Ian Geoffrey Stimpson via Flickr.com
Colemanite is a calcium
borate hydrate, which can form monoclinic
crystals or be compact, granular or massive. It can be white, grey or
yellowish brown in colour. Like many other minerals in this group, it
forms in evaporative deposits from other minerals. It was named after
the owner of a Californian mine where it was first discovered.
Kernite. By David Casteel
Kernite is a
sodium borate hydrate, which can form short, prismatic,
transparent, colourless, very large crystals, but is more commonly
found in cleaved masses with a fibrous structure. It is a colourless
mineral when white, but can be white when its crystals
are covered by tincalconite - a dehydration product of borates
that builds a white, opaque surface film on the crystal surface. It
forms in mineral veins and irregular masses in evaporative deposits,
where it is usually associated with other boraten minerals. It can also
be found as crystals in shale.
Ulexite. By Kathy__ via Flickr.com
Ulexite is a
sodium calcium borate hydrate. It is most often found in
white, silky, acicular lenslike or rounded crystal aggregates, but can
also form colourless, vitrous, fibrous, parallel crystals or tufted
masses. It is found in evaporative deposits in desert lake
beds, where it forms from boron rich fluids.