Ontario banded iron formation main content.

Ontario banded iron formation

Ontario Banded Iron Formation AMNH/R.Mickens

Exhibition Text

This banded iron formation comes from a rock unit 60 meters thick that formed over a 50-million-year period, from 2.736 to 2.687 billion years ago. The red bands are silica-rich, composed primarily of jasper, and the black bands contain the iron oxide mineral magnetite. Some geologists have interpreted the alternating layers as seasonal variations in the amount of oxygen available to oxidize and precipitate the dissolved iron.  

Donated by the Dofasco Company, Strathy Township, Ontario, Canada

For Educators

Topic: Earth Science

Subtopic: Earth Formation/Evolution

Keywords: Geology, Stratigraphic--Precambrian, Jasper, Metamorphic rocks, Magnetite

Audience: General