Hematite
By Bob Farrar
Hematite is the most important ore of iron, and so is of tremendous economic importance. As such, hematite may seem like a rather mundane mineral, but it is also an interesting mineral for collectors, and is sometimes used in lapidary work. Hematite consists of ferric oxide, Fe2O3. It crystallizes in the hexagonal system, but good crystals are relatively uncommon. Hematite varies in color from red to black, but the streak is typically red. The red color of the streak is the root of its name, which comes from the Greek haimatitis, meaning “blood red”. Hematite also varies greatly in hardness, from soft, earth material with a hardness of about 1, to compact material with a hardness of 6.5. It is a fairly heavy mineral, with a specific gravity of 4.9 to 5.3. The red streak of hematite is its most important distinguishing characteristic. Streak distinguishes hematite from limonite and ilmenite, and a lack of magnetism distinguishes it from magnetite. Crystallized hematite, commonly known as “specular hematite” is fairly distinctivein appearance, commonly forming flat, hexagonal plates. Soft, red material is known as ochre, and has been used as a pigment since prehistoric times. Hematite occurs in a variety of environments. Vast sedimentary deposits are thought to have been formed billions of years ago when the Earth's atmosphere first became rich in oxygen. The availability of oxygen caused the iron to “rust” out of the
ocean. These and metamorphic formations derived from them are major sources of iron ore. Major iron ore localities include the Lake Superior region of the US, Brazil, Venezuela, China, and Liberia. While iron ore is of great economic importance, it is usually not of much interest to mineral collectors. However, hematite also occurs in many more interesting forms. Among the most famous are clusters of thin hexagonal crystals up to 10 cm across from alpine cleft formations in Switzerland. These and similar specimens from other localities are known as “iron roses”. Well crystallized specimens are found in the iron ore producing districts near Belo Horizonte, Brazil. Also in Brazil, hematite crystals form the base on which needles of rutile grow and become embedded in rutilated quartz. Knobby masses of hematite known as “kidney ore” are found in England as well as Brazil. Hematite with an attractive iridescent tarnish is found at Graves Mountain, Georgia. Other worldwide and US localities are too numerous to mention. Locally, hematite is found in a number of sites, including Havre de Grace in Harford Co., Mineral Hill in Carroll Co., and the Ben Murphy Mine in Howard Co.
ocean. These and metamorphic formations derived from them are major sources of iron ore. Major iron ore localities include the Lake Superior region of the US, Brazil, Venezuela, China, and Liberia. While iron ore is of great economic importance, it is usually not of much interest to mineral collectors. However, hematite also occurs in many more interesting forms. Among the most famous are clusters of thin hexagonal crystals up to 10 cm across from alpine cleft formations in Switzerland. These and similar specimens from other localities are known as “iron roses”. Well crystallized specimens are found in the iron ore producing districts near Belo Horizonte, Brazil. Also in Brazil, hematite crystals form the base on which needles of rutile grow and become embedded in rutilated quartz. Knobby masses of hematite known as “kidney ore” are found in England as well as Brazil. Hematite with an attractive iridescent tarnish is found at Graves Mountain, Georgia. Other worldwide and US localities are too numerous to mention. Locally, hematite is found in a number of sites, including Havre de Grace in Harford Co., Mineral Hill in Carroll Co., and the Ben Murphy Mine in Howard Co.
|
|
|
|