I would have called it malachite, maybe it effervesces due to some carbonate in the rock? Whip out your portable XRD!

Fair enough, just razzing anyhow.

Maybe in elementary school... but I still have them so it likely worked. When I lived in town they started putting it in the drinking water so maybe that helped!

For me, I have a monomineralic rock in my head made of apatite.

Holy shit, labradorite is beautiful. We have a company here in town that does 'granite' countertops and I was always in love with it since my undergrad. I want countertops of it. However, the correct thing to say would be your favourite mineral is feldspar - no?

Another one to give them is amtospheric CO2 over time. I recall one graph in my undergrad where it also had significant anthropological events on it like when the industrial revolution started etc.

I'm here, lurking. Make a rock ID thread!

Maybe I'll go out to my collection and put up some tests.