Me and some of my friends were wondering what exactly is the white coating we can see on chalcedony that has been deposited by a river during quartenary (and so the original material is damaged and has a lot of cracks in it). This is an example:
So far everything I found was this link: http://www.treasurenet.com/forums/north-american-indian-artifacts/238703-agate-arrowhead-white-patina-question.html
These people describe it as "patina" or "chalcedony weathering". I am wodering what is the process and how can we easily chemically or physically explain it ?
I think it must be some kind of weathering.. similar to oxidation. I believe that it is opalization. What do you think ? I saw this forming on many agates all over the world, but only at these, that were eroded from the mother rock, transported and deposited. It is especiially common on deposited chalcedony.