Cobalt canyon in the side of a mountain. The firm Calera Mining Company started production at the site. The stable form of cobalt is produced in supernovas through the r-process. It comprises 0.0029% of the Earth's crust. Free cobalt (the native metal) is not found on Earth because of the oxygen in the atmosphere and the chlorine in the ocean. Both are abundant enough in the upper layers of the Earth's crust to prevent native metal cobalt from forming. Except as recently delivered in meteoric iron, pure cobalt in native metal form is unknown on Earth. The element has a medium
Cobalt aminopeptidase 2, an enzyme that occurs in humans and other mammals that does not use the corrin ring of B, but binds cobalt directly. Another non-corrin cobalt enzyme is nitrile hydratase, an enzyme in bacteria that metabolizes nitriles. Cobalt is an essential element for life in minute amounts. The LD value for soluble cobalt salts has been estimated to be between 150 and 500 mg/kg. In the US, the Occupational Safety and Health Administration (OSHA) has designated a permissible exposure limit (PEL) in the workplace as a time-weighted average (TWA) of 0.1 mg/m. The National Institute for Occupational Safety and