Hematite
Chemical Composition |
Fe2O3 - Ferric Iron oxide |
Color |
Black to silver gray, in earthy forms is red to brown |
Cleavage |
none |
Hardness |
5 - 6 (hard) in most varieties, but earthy variety is very soft (<2) |
Specific Gravity |
5.3 (feels heavy, average for a metallic mineral) |
Luster |
wide range from splendent metallic to dull earthy |
Streak |
red brown to rusty red |
Hematite is one of the most abundant minerals on Earth's surface and in the shallow crust. It is an iron oxide with a chemical composition of Fe2O3. It is a common rock-forming mineral found in sedimentary, metamorphic, andigneous rocks at locations throughout the world.
Hematite gets its name from the Greek word for blood, haima, because of its reddish color. This is one of the types of iron ore that has very high iron content, and although the iron content of hematite itself islower than that of magnetite, the mineral sometimes occurs in higher-grade deposits, often referred to as direct-shipping ore (DSO). This means that, due to its high iron content, such hematite ores may be mined and extracted with a fairly simple crushing and screening process before it is exported.
Hematite is the most important ore of iron. Although it was once mined at thousands of locations around the world, today almost all of the production comes from a few dozen large deposits where significant equipment investments allow companies to efficiently mine and process the ore. Most ore is now produced in China, Australia, Brazil, India, Russia, Ukraine, South Africa, Canada, Venezuela, and the United States.
Hematite has a wide variety of other uses, but their economic significance is very small compared to the importance of iron ore. The mineral is used to produce pigments, preparations for heavy media separation, radiation shielding, ballast, and many other products.
Physical Properties of Hematite
Hematite has an extremely variable appearance. Its luster can range from earthy to submetallic to metallic. Its color ranges include red to brown and black to gray to silver. It occurs in many forms that include micaceous, massive, crystalline, botryoidal, fibrous, oolitic, and others.
Even though hematite has a highly variable appearance, it always produces a reddish streak. Students in introductory geology courses are usually surprised to see a silver-colored mineral produce a reddish streak. They quickly learn that the reddish streak is the most important clue for identifying hematite.
Hematite is not magnetic and should not respond to a common magnet. However, many specimens of hematite contain enough magnetite that they are attracted to a common magnet. This can lead to an incorrect assumption that the specimen is magnetite or the weakly magneticpyrrhotite. The investigator must check other properties to make a proper identification.
If the investigator checks the streak, a reddish streak will rule out identification as magnetite or pyrrhotite. Instead, if the specimen is magnetic and has a reddish streak, it is most likely a combination of hematite and magnetite.
Composition of Hematite
Pure hematite has a composition of about 70% iron and 30% oxygen by weight. Like most natural materials, it is rarely found with that pure composition. This is particularly true of the sedimentary deposits where hematite forms by inorganic or biological precipitation in a body of water.
Minor clastic sedimentation can add clay minerals to the iron oxide. Episodic sedimentation can cause the deposit to have alternating bands of iron oxide and shale. Silica in the form of jasper, chert, or chalcedony can be added by chemical, clastic, or biological processes in small amounts or in significant episodes. These layered deposits of hematite and shale or hematite and silica have become known as the "banded iron formations" (see image).
Chemical composition:
Fe Total 55.00 % Min
SiO2 10.50 % Max
AL2O3 2.50 % Max
S 0.1 % Max
P 0.1 % Max
Physical specification:
Moisture 3.0 % Max
Grain Size 10-30 MM = 98.8% > 30 MM 1.2%
0-10 MM = 53.0% <150 MM 7.0%