Book 27, Question 39
Why do bismuth crystals look like staircases?
Bismuth is a metal that grows into square spiral shapes called hopper crystals.
The edges grow faster than the middles, which leaves stepped hollows like a staircase. A thin layer of oxide forms on the surface, and light reflecting from it makes rainbow colors. Scientists grow bismuth crystals in labs by carefully melting and cooling it. Don't try melting metal at home.