Ontario banded iron formation
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
Topic: Earth Science
Subtopic: Earth Formation/Evolution
Keywords: Geology, Stratigraphic--Precambrian, Jasper, Magnetite, Metamorphic rocks