A zinc coin
Zinc is an essential trace element for living things. It has some germicidal properties and it is toxic in large quantities. Zinc pennies should never be swallowed.
Source
Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:
"General%2520Chemistry/Chemistries%2520of%2520Various%2520Elements/Transition%2520Metals."
http://en.wikibooks.org/wiki/General_Chemistry/Chemistries_of_Various_Elements/Transition_Metals%23Families
Wikibooks
CC BY-SA 3.0.