Many an element collector started out by coming across these little souvenirs bought at museum gift stores or rock shops. The weird Escher-like formations happen when molten bismuth begins to solidify at an uneven pace along its surfaces. As the surfaces collide they change directions at right angles according to its lattice structure and in so doing create the odd-looking walls and stair steps. The iridescence is due to very thin layers of oxidation and are allowed to occur for purely aesthetic reasons; a little thicker here, a little thinner there in each case a different color is produced due to light refraction.
A beautiful crystal will be included in your container weighing between 5-10 grams.