What the heck is 'green rust' ?

So green rust offers hope for the future.  But that beggars the question -- what exactly is 'green rust' ?  It appears that it is an oxidation product of iron (Fe), but rather than the normal case of Fe³⁺ (which creates red rust), this is rust utilizing Fe²⁺. 

I got that from this:  Iron (II) hydroxide

"If the solution was not deoxygenated and the iron reduced, the precipitate can vary in color starting from green to reddish brown depending on the iron(III) content. This precipitate is also known as "green rust" in the crystal lattice of which iron(II) ions are easily substituted by iron(III) ions produced by its progressive oxidation."

So it turns out that recently natural iron (II) hydroxide was found, and it is named fougerite.

And apparently fougerite gives us hope:

 Evidence of oceanic "green rust" offers hope for the future

But why?  WHY?

This is why:

"The high reactivity of green rust is the reason it could be so much help in cleaning up polluted sites. The rust reduces elements like chromium, uranium and selenium, significantly reducing their solubility and mobility in the environment, and in some cases absorbing them into the rust's molecular structure."

So now I know.  And now anybody reading this knows, too.