Biotitic Mafic Dike at the Blackbird Cobalt-Copper Mine

USGS scientist John Slack holds his hammer to a biotitic mafic dike, intruded into twice-folded banded siltite, exposed in the Hawkeye adit of the Blackbird cobalt-copper mine, in the Salmon River Mountains of east-central Idaho. Biotite is a type of mica, and mafic refers to a high magnesium and iron content.