Hematite

specimen number:
2062134

location:
Aurora Mine, Ironwood, Michigan, USA

description:
A good example of what is often referred to as needle iron ore. In good condition all around. At one time this piece was part of the collection of the A. E. Seaman Museum at Michigan Tech University.

The Aurora Mine, located in Ironwood, Gogebic County, Michigan, was one of the premier producers of the Gogebic Iron Range. Geologically, the mine exploited the Paleoproterozoic-aged Ironwood Iron Formation, which consists of alternating layers of chert and iron-rich minerals such as hematite and magnetite. These deposits were concentrated into high-grade "soft" ores by the action of descending groundwater, which leached away silica within structural troughs formed by the intersection of the iron formation and intrusive igneous dikes. Historically, the Aurora Mine was opened in 1884 and quickly became a major industrial site, eventually being managed by the Oliver Iron Mining Company, a subsidiary of U.S. Steel. The mine operated through both open-pit and deep underground methods, with production continuing consistently until its closure in 1948. Throughout its lifespan, the Aurora was recognized for its massive output and its role in establishing the Gogebic Range as a vital supplier for the American steel industry during the late 19th and early 20th centuries.

Needle ore is a distinctive morphological variety of hematite characterized by the growth of extremely thin, acicular (needle-like) crystals. Geologically, these crystals often form through hydrothermal processes or the slow precipitation of iron oxide from mineral-rich fluids within rock cavities and vugs. Unlike the common massive or specular varieties of hematite, needle ore appears as delicate, radiating clusters or "sprays" of fine metallic fibers that can sometimes resemble dark, metallic fur. These needles are typically dark gray to black with a bright metallic luster, though they still produce the characteristic reddish-brown streak typical of all hematite when powdered. This variety is particularly sought after by mineral collectors for its geometric precision and fragile beauty, with notable specimens historically found in the iron districts of Great Britain, such as Cumbria, and certain mines within the Lake Superior Iron Ranges of North America.

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