Selenium
Selenium is very rarely found as an element in the ground. Most selenium in soil is in a very tiny amount. It is easily washed away. It is in very small amounts in the human body. Selenium is found most in sulfide ores like pyrite. This selenium is in selenides. Selenium is gotten as a byproduct. Sometimes selenium is concentrated in plants. It can also be leached into rivers when copper is mined. Too much selenium is bad for a river. Some coal has selenium in it.