Bismuth
Bismuth Symbol Number 83 on the periodic table Bismuth has long been considered as the element with the highest atomic mass that is stable. However, in 2003 it was discovered to be weakly radioactive with a half life of more than a billion times the estimated age of the universe. ( Wikipedia ) The melting temperature of bismuth is 520.6°F When melted and partially hardened bismuth if solidified into beautiful crystals. The full cycle of ingot to crystals in the link: https://www.youtube.com/watch?v=v8KYZHMkTHw The crystals look like squares growing upwards and spiraling around. Bismuth crystals rarely form in nature, but they do form in incredibly shiny chunks Bismuth is very fragile and brittle, so a few light hits with a hammer snaps apart the chunk like a twig The approximate price of about one pound of Bismuth is 13 USD, from ROTOMETALS To grow bismuth crystals you will also need a crucible, though a pot that you intend to never use ag