"This is a Adamite from Ojuela Mine, Durango, Mapimi, Mexico. I first owned this adamite back in the early 1990s and was happy to find it turn up again, instantly remembered because of the interesting shape of the "wave" of adamite atop a nicely balanced matrix (I am biased, having done a risky trim on a bigger specimen using a hammer and chisel at the time).
Click here for more info on The Arkenstone."