Take a close look at Banded Jasper

by Bill Teftt. Photography by Ken Hupila of Snotty Moose Studio.

Rock from banded iron formations can be over 200 million years old and still look just as beautiful as ever. Whenever you get near the underground iron mines that used to operate in northeastern Minnesota, you can experience the banded iron formation or BIF. Waste rock will be found that didn’t meet the marketable characteristics of iron ore and certainly here on the Vermilion Range, a good deal of the waste will be Ely Greenstone. While greenstone had its origins under sea water at around 2.7 billion years ago, iron, within the same area, the massive hematite was the mineral – the iron ore - that was removed to make steel. However the waste rock that catches the most attention has bands of hematite and bands of chert.
In many places around the earth between 1.8 and 2.5 billion years ago, BIFs were forming. The animal life of today live and depend on a world that has an oxygen rich atmosphere. That oxygen supply did not always exist on earth. There was a time before cyanobacteria, algae and other early oxygen producing organisms existed when oxygen was not always present or was not available.
For banded iron formation to develop there must be oxygen. Iron (Fe) or Silica (SI) may be present in the water of the oceans but until oxygen is available to combine with them, they stay in solution. When dissolved iron or silica or other elements are oxidized they precipitate out, settling to the sea floor. Over long periods of time the sea bed layers of iron oxides became hematite or magnetite rich in iron. The hematite is a rich gray color easily seen in banded rocks. Often alternating among varied thicknesses of layers was the silica-rich oxides often referred to as chert or jasper.
The resulting rocks are waste because there was no practical means to separate the potentially valuable hematite from the chert. These rocks however represent the most distinctive evidence of iron rich areas by a distinctive appearance the BIF label is applied to the iron formations. The specific banded rock is often called banded jasper with jasper being the red colored chert due to some iron content. However, cherts can vary from nearly white to almost black.
Putting a piece of banded jasper in water really brings out its colors. Looking at it closely with the sun shining on it and with the use of a magnifying glass can reveal even more aspects of its sedimentary history of built up layers. Like much of the 2 billion old geologic material making up parts of the earth, not all banded jasper and associated rocks look alike. Some may have experienced little alteration over that time span and others may have experienced a lot of change. Exposure to erosion, glaciers, extreme heat or pressure, chemical weathering, etc. are all potential parts of a piece of banded jasper’s life story.
That story may continue in a rock garden or a piece of jewelry or a lucky pocket stone or on display for study in a science classroom. Whatever the contact, it is fortunate to make the acquaintance
and challenging to understand how these rocks of such an old age originally came into existence.
If you have questions, observations, reports or requests for this column, contact the Ely Field Naturalists at http://groups.google.com/group/elyfieldnaturalists. If you would like to join in the postings or get information about group events contact Bill Tefft by email at efnbill@gmail.com or phone at 218-235-8078. View more of Ken Hupila’s pictures at www.snottymoose.com.