Green Crystals in ferric-chloride
Ferric chloride is known as FeCl3.
On this wikipedia page:
sur cette page :
The reaction of FeCl3 with printed circuit boards is given in the "Uses" section:
FeCl3 + Cu → FeCl2 + CuCl
FeCl3 + CuCl → FeCl2 + CuCl2
A quick search on google-image yiels interestings results, with pictures very similar to the crystals on this page.
The crystals will form when the CuCl2 is hydrated, as is the case with this experiment.
On the other hand, FeCl2, the other product of the reaction, is also green (but lighter). The crystals on this page are perhaps a mix of CuCl2 and FeCl2...