Life in a Geode

When I taught the occasional class for youngsters (elementary level), one activity I often did was egg-shell geodes: take a washed eggshell, hopefully half the shell or more, and fill it to the brim with saturated copper sulfate solution. As the solution cools and evaporates, you get beautiful blue crystals filling the shell over a period of days. Copper sulfate is not hugely toxic, but you don't want to breathe the dust or ingest any of it- and with this age group you need to make it very clear what the ground rules are regarding safety concerns. I generally asked parents to send in a note allowing the student to take their geode home, or (for some of the summer camp-type of classes), simply hand it off to the parent at the end.

So the dust created as spectators tramp around in this project is a bit of a concern to me, but still... very cool! Full discussion and video at the linked site.

For you geo-types, does copper sulfate ever crystallize as a mineral in the weathering zone above copper sulfide deposits? I don't think I've ever seen it listed as a mineral, but I would think it might occasionally be left behind in arid environments, such as the southern Arizona copper belt. Also, the name I remember for such weathering zones is "gossan," but in googling that term, it apparently applies specifically to iron oxide/hydroxide weathering remnants. What term would you apply to weathered copper deposits containing the typical suite of malachite, azurite, chrysocolla and so on?

Followup: Bunch more pictures here

Followup Wed. 11/19: Here