Conundrum

This is a piece of Bismuth that I bought from a market stall on Sunday. The man I bought it from told me he thought it came from Mexico, but on returning home, I found out that crystals like this are very rare in nature. This has certainly been grown in a laboratory. My wife did say that she saw the man smiling to himself as I bought it.

These are "hopper" crystals that form due to the disparity of growth rates between the crystal edges and the crystal faces. You see square shapes in this direction, but if you look end on you realise that it is a trigonal crystal, with a barbed, arrow-head appearance. It also has a bluish metallic lustre which is not that apparent in the photo. The way that the threefold and fourfold symmetry is resolved is the most fascinating thing about it, like a solidified Escher conundrum.