This is a truly spectacular (for both size and form) crystal of a little-known borate. It is an evaporite mineral that forms by the evaporation of water from desert lakes enriched in boron (as here in the eponymous locality: Boron, California). Here, it has formed an absolutely huge crystal, and remarkably transparent - even rather attractive. It shows very sharp faces and good luster. Ex. Minette collection obtained from Jim Minette (who collected it some years before) in the mid 1990s.