Taconite
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2008-07-11T09:52:31Z
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[[Image:Taconite.jpg|thumb|300px|Taconite]]
'''Taconite''' is an [[iron]]-bearing, high-[[silica]], [[flint]]-like rock. It is a [[Precambrian]] [[sedimentary rock]] referred to as a [[banded iron formation]] due to the typical alternating iron-rich layers and [[shale]] or [[chert]] layers. The very finely dispersed iron content, present as [[magnetite]], is generally 25 to 30%. In the late 19th and early 20th centuries, available [[iron ore]] was of such high quality that taconite was considered an uneconomic waste product. After [[World War II]], most of the high grade ore in the [[United States]] had been mined out, and so taconite was turned to as a new source of iron. To process taconite, the ore is ground into a fine powder, the iron is separated from the waste rock by using strong magnets, and then the powdered iron concentrate is combined with [[bentonite]] clay and limestone as a flux and rolled into pellets about one [[centimeter]] in diameter that are approximately 65% iron. The pellets are heated to very high temperatures to [[oxidize]] the magnetite (Fe<sub>3</sub>O<sub>4</sub>) to [[hematite]] (Fe<sub>2</sub>O<sub>3</sub>) for further processing. [[Edward W. Davis]] is credited with developing this process.
The [[Mesabi Range|Mesabi Iron Range]] region of the American state of [[Minnesota]] is a major production area. The taconite iron concentrate is hauled by [[railroad]] through [[Silver Bay, Minnesota|Silver Bay]], [[Two Harbors, Minnesota|Two Harbors]] and the [[Twin Ports]] of [[Duluth, Minnesota]] and [[Superior, Wisconsin]], all on [[Lake Superior]]. The ore is generally shipped by [[lake freighter]]s to other locations on the [[Great Lakes]]. Many steelmaking centers are located near [[Lake Erie]]. From about [[1900]] through [[1992]], great machines called [[Hulett]] ore unloaders performed the task. Self-unloading ships later made the Huletts obsolete.
==Taconite and Human Health==
The Minnesota Department of Health has launched a study to determine whether taconite fibers and dust can cause or exacerbate lung conditions such as [[mesothelioma]] and [[asbestosis]] which occur following asbestos exposure. Because [[asbestos]] was common in the taconite mining and processing industry, the study will attempt to determine what, if any, influence taconite fibers may have played. This will be the second study of the issue that the MDH has conducted. A 2003 study of taconite miners concluded that the most likely cause of 14 of the 17 cases of mesothelioma was contact with asbestos. However, since the conclusion of that study, 35 additional cases of the disease have been diagnosed. Mesothelioma occurs at twice the expected rate in the region of Minnesota known as the [[Iron Range]].
<ref>{{cite news
| last = Hemphill
| first = Stephanie
| title = Researchers look for links between taconite and mesothelioma
| publisher = Minnesota Public Radio
| date = [[2007-06-08]]
| url = http://minnesota.publicradio.org/display/web/2007/06/07/mesostudy/
| accessdate = 2007-07-18 }} </ref>
==References==
*[http://www.dnr.state.mn.us/education/geology/digging/taconite.html Minnesota DNR]
*[http://www.tc.umn.edu/~smith213/ma.htm Magnetite in taconite]
*[http://geography.miningco.com/library/misc/ucmesabi.htm Mesabi Iron Ore Range]
*[http://www.silverbay.com/history.htm/ Silver Bay, Minnesota]
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{{mineral-stub}}
[[Category:Economic geology]]
[[Category:Mining]]
[[Category:Iron minerals]]
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[[ja:タコナイト]]