During a cycle through East Galway during a strangely sunny day in the dead of winter 2003, I met some horses and saw a lot of ruined buildings.
A few days later, during the same sunny spell, I visited a chemical storage facility in Foynes port that my father helped to build. The green stuff he is breaking up with his JCB is ferrous sulphate (heptahydrate).
en.wikipedia.org/wiki/Iron%28II%29_sulfate
Absorption of water from the air causes the crystals to solubilise slightly and reform in a weak lattice. This weak lattice can be broken up, and crystals scooped up, ready for transfer to trailers for transport.
The rust coloured liquor is some water of deliquescence which has been released from the crystals, presumably rich in free iron, explaining its colour.
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