SPECULAR HEMATITE

Should this mineral be called “spectacular” hematite?  It is highly prized by collectors for its sparkle (as seen in Figure 1). Its chemical formula is Fe2O3 [= ferric oxide]. Hematite is the most important and widely used source mineral for iron. This mineral is mainly a sedimentary mineral, which gets altered by ground water. The hardness of this mineral is 5 to 6. It can be polished (as a gemstone) even though it is easily scratched or chipped. It also readily alters to the iron-mineral limonite.

Hematite is the most important and widely used source mineral for iron. More that 90 percent of iron in the USA is from hematite ore.

There are three types of hematite: shiny black (= specular hematite), brownish, and blood red. Vast deposits of it occur in the Lake Superior area. It is also found from New York to Alabama, as well as England, Switzerland, Italy, and Brazil.  The extensive Clinton iron beds of late Silurian age crop out over a length of about 700 miles in New York, Pennsylvania, and Alabama.

Figure 2 (see image below) refers to one way this mineral is determined: rub it on a streak plate (this is a common practice among mineralogists because certain minerals have a distinctive streak color, which can be different than the exterior color of a mineral).  

References

Berrry, L.G. and B. Mason, B. 1959. Mineralogy. Concepts, Descriptions, Determinations. W.H. Freeman and Company. San Francisco. 630 pp.

Sorrell, C.A. 19xx. Rocks and Minerals. Golden Nature Book. A field guide to rocks and minerals. Golden Press, New York. 630 pp.

Figure 1. Specular hematite. 43 mm length, 23 mm width.

Figure 2. The reddish residue left by hematite when it is rubbed against a two-inch long  “streak plate” [consisting of  porcelain]. Streak plates are commonly used in the identification of minerals.