Jaspillite

Jaspillite, or "jaspilite", is a chemical rock formed similar to chert. It is usually iron rich. It also has the name "jasper taconite". 
Jaspillite is typically a layered mixture of hematite and quartz. It is common in the banded iron formation rocks of Proterozoic and Archaean age in the Canadian shield of North America.
Jaspillite is also a sedimentary rock.in certain lead-zinc ore deposits.
It is used as a gemstone.