I have left very used ferric chloride in plastic recipient containing Ferric Chloride for many months, and when I decided to clean it up, I discovered that thousands of small green crystals had formed in it.

(Click on the picture to see closer. Sorry for the bad image quality.)

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Here are a few closeups of the crystals:

I think those crystals are very pretty. They are transparent, very long and fine. Their color reminds me of the artificial kryptonite seen in one of the Superman movies.

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I have dissolved a few crystals in a small quantity of water, and looked at it with a microscope. New crystals have formed again.

Here are pictures taken with back lighting:


A some places, the crystals were so thick that light would not pass through. I tried lighting from the other side, and it gave nice results:



As we can see, the crystals look the same as the bigger ones in the microscope, but they are of course smaller.

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I would like to know what is the exact composition of those crystals. I think it must be copper oxide or something similar.

If you can tell me more, write me. raph@raphnet.net. Thank you.

UPDATE!
Mr. Reventlov sent me the following suggestion which I think makes sense:
Ferric chloride is known as FeCl3.
On this wikipedia page:
sur cette page :
http://en.wikipedia.org/wiki/FeCl3
The reaction of FeCl3 with printed circuit boards is given in the "Uses" section:

FeCl3 + Cu → FeCl2 + CuCl
followed by
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...


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