Dylan Ford wrote: "Kenneth - I am not entirely comfortable speculating on
this. According to
internet search Borax has 11% available Boron, but I have no idea what might
be represented in the other 89%."
Dylan,
The empirical formula for the mineral, Borax, is Na2B405(OH)4-8H20.
Sodium (Na) comprises 12.06%, Boron 11.34%, Hydrogen 5.29% and Oxygen
71.32%.