Bismuth
Bismuth has many interesting properties. It has a relatively low melting point, 520 degrees Fahrenheit making it useful for alloying with other metals.
Bismuth has a very low thermal conductivity, expands as it cools and has a very high diamagnetic value. Unlike lead it is a brittle metal, it will break onto crystalline chips when hit with a hammer.
How it is used
Bismuth is an organically-safe substitute for lead. Having the same density of lead but is non-toxic, used to make shot for shotgun shells, fishing lures and low melt alloys. We have a lot of customers who will buy the Bismuth to "grow" crystals. They will melt the Bismuth which causes it to become a multi colored shape.
Every Bismuth piece will produce a different shape and color when melted.
For example: