Term: mica slate (mining)
Definition:
One of the most stratified rocks belonging to the primary class, composed of mica and quartz, the mica being in layers makes it appear to predominate.
View pictures relating to mining at Wisconsin Historical Images.
[Source: "Glossary of Miners' & Mineral Terms" in St. John, John R. A True Description of the Lake Superior Country ... (New York, W. H. Graham, 1846).]
