Hi,
French GRIS means grey, but the GRISON breccia is always dark red-brown. The breccia iron-oxide cement also exist in the from of grit or gravel.
English GREISEN is ponounced GRISON in french.
Saxon GREIS, GREISS; GREISSEN and derivatives means to split and also has the sense of grit or gravel. French GRES (sandstone) has also the same root. So does the english word GRIST too.
Grison was only used as ore until 1066, when its solid fractions were thereater used as a building stone, mainly for building Norman churches, where none had existed previously.
This was precisely the moment when Henry de Ferrers, an ironmaster Baron became aquainted with english mining techniques. And when English monks such as Orderic Vital were sent to Normandy.
In the de Ferrers mining area of Normandy, there was no other hard building stone available, and buildings were made from timber, wattle and daub, with some flint.
The Anglo-Normans built the fortified town of Verneuil mainly using grison, so the coincidence is very revealing.
GREISENS are common in Devon, where the village of Birland (Bere Ferrers) was a major mining centre.
Devon & Cornwall miners spoke anglo-saxon and kernow dialect...
Miners frequently travelled between Bohemia, the Harz and Devon, exchanging vocabulary as techniques improved, as they were considered freemen, with their own systems to regulate their trade.