There are a number of gems that could be considered to be poisonous. Because of their chemical content, these gems are poisonous to some degree. Among the elements that make these gems poisonous are Arsenic, Lead, Mercury and Sodium Fluorine. Most of these gems are safe under normal circumstances but all should be handled with caution. Always wash hands after handling. Also see the Radioactive Gems information page for other gems with Health Warnings.