Well, I did write a guide on this large amount of Chalcanthite from Poland that is influxing into eBay but for some reason it has mysteriously vanished. ***Funnily enough, my original guide has now appeared!!***
However, let me reiterate....
So, let me please advise you - this material is fake. Chalcanthite occurs in arid copper mineral deposit regions, usually as a bluish crust or VERY rarely a small ram's horn presentation - it NEVER occurs as these gaudy and florid bathtub-grown crystals that are either grown on, or stuck onto rocky matrix and come from Poland.
Please see pics!! This is REAL Chalcanthite.

I received quite an unpleasant email from a seller when I remarked on his fakery.  I suspect that possibly they were responsible for the removal of my original guide to this mineral.
Chalcanthite and the rubbish these people are selling are chemically identical - hydrated copper sulphate - however, we have all grown crystals at home as kids by dissolving stuff in water, making a saturated solution and watching the crystal grow... the rubbish from Poland is done exactly the same way - except they tell you it comes from the "copper mines".
Also note that the buyer IDs are always kept confidential so they cannot have anyone advise them accordingly.
And, if you buy one of these rather nasty toxic rocks, if you live in a dry part of the world, it will become partially anhydrous at the edges, turn pale bluish and crumble.
If you want to look at what REAL Chalcanthite looks like then Google for images.

DO NOT FORGET THAT THIS STUFF IS TOXIC!!