What I believe is an amethyst geode (roughly 6" = 15.24 cm across) from somewhere in the Carpathian Mountains
contains an oval-shaped inclusion of material with what look like pits of green corrosion:
Apologies for the lack of scale in these shots; it's roughly 1" (25 mm) across (on the short axis, as marked in the picture) and 2" (51 mm) long. It's also apparently magnetic; notice the small, rare earth magnet attached.
In trying to satisfy the posting guidelines, I reckon the inclusive rock (not the surrounding geode) has dull lustre, smooth grain, it's brittle and cracking a little, and I estimate its Mohs hardness at 3 to 5 (it cannot be scratched by fingernail but could be scratched by a steel knife).
It's so brittle that a little piece came off, which shows that the green material seems the most magnetic, with the grains of green material sticking to the magnet: