Hi,
From various on-line dictionairies we also get :
Greis, Griess, griez, greisen, greissen, grysla, grizzly, grès, grist; (from ancient northern european languages) ;
with the senses of split, grit, gravel, sandstone, all turning around the notion of rocks & crushing, indeed grizzlys are to this day ore grading devices...
Grison is a loose or consolidated iron ore, whose etymology has always been a mystery :
(Greisen is grey quartz often with reddish bands, similar in appearance to Norman iron-bearing sandstones).
A possible explanation?