Jaspellite, Tower-Soudan mine area, northern Minnesota

Banded iron formation (BIF) is characterized by alternating iron-rich and silica-rich laminae. Jaspelite is a particularly spectacular variety, rich in red hematite. Jaspelite is very interested structurally, for folds and faults are so conspicuous, given the prominence of contrasting layers. Banded iron formations and jaspelites are restricted to ancient times, and many believe that their origin required an atmosphere deficient in oxygen. Thus, as iron and silica were transported in streams from the land into oceans, biological processes permitted them to precipitate as we see them today.

I collected this in 1992 on a Carleton College geology field trip to northern Minnesota.  I was a visiting professor at Carleton at the time.  I wish I had a room full of jaspelite specimens, because colors, textures, and geometries are so rich; and the mineralogy (for a sedimentary rock) so unusual. 

Age & Formation
Paleoproterozoic age, ~1.7 Ga