<p>Pyrite crystals in magnetite-quartz banded iron formation in the Precambrian of Ontario, Canada.
</p><p>Whitish = quartz-rich
Dark gray = magnetite-rich
Brassy-gold = pyrite (FeS2)
</p><p>The outcrop shown here consists of BIFs - banded iron formations.  BIFs are unusual, dense sedimentary rocks consisting of alternating layers of iron-rich oxides and iron-rich silicates.  Most BIFs are Proterozoic in age (although some are Late Archean), and do not form today - they're “extinct”!  Many specific varieties of iron formation are known, and some are given special rock names.  For example, jaspilite is an attractive reddish &amp; silvery gray banded rock consisting of hematite, red chert (“jasper”), and specular hematite or magnetite.  This outcrop has magnetite-quartz BIF.
</p><p>Because of their age, most BIFs have been around long enough to have been subjected to one or more orogenic (mountain-building) events.  As such, most BIFs are folded, faulted, and/or metamorphosed to varying degrees. 
</p><p>BIFs are known from around the world, but some of the most famous &amp; extensive BIF deposits are found in the vicinity of North America’s Lake Superior Basin.  Many BIFs have economic concentrations of iron and are mined - they are the most important variety of iron ore on Earth.
</p><p>The rocks at this locality are structurally tilted.  Small-scale folds and faults are present in the area.  Published literature refers to the folding here as soft-sediment deformation.
</p><p>The brassy gold-colored crystals are pyrite ("fool's gold), which is iron sulfide, FeS2.
</p><p>Stratigraphy: Temagami Iron-Formation, lower Neoarchean, ~2.736 Ga
</p>
Locality: Temagami North Outcrop - roadcut on the western side of Rt. 11, immediately north of town of Temagami, eastern Ontario, southeastern Canada (47° 04’ 06.70” North latitude, 79° 47’ 26.08” West longitude)
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/47445767@N05">James St. John</a>
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/jsjgeology/40841843323/">Pyrite crystals in magnetite-quartz banded iron formation (Temagami Iron-Formation, Neoarchean, ~2.736 Ga; Temagami North roadcut, Temagami, Ontario, Canada) 10</a>