Chromium
Chromium (Cr) is a hard, bluish metallic element. The only ore of chromium is the mineral chromite and 99 percent of the world’s chromite is found in southern Africa and Zimbabwe. Geologists estimate that there are about 11 billion tons of mineable chromite ore in the world, enough to supply the current demand for hundreds of years. It is mostly used for making stainless steel and other metal alloys.
Type
Element (Minerals/Ores of)
Mineral Classification
Oxide
Chemical Formula
(Fe, Mg)Cr2O4
Streak
Brown
Mohs Hardness
5.5
Crystal System
Isometric
Color
Black to brownish black; brown to brownish black on thin edges in transmitted light
Luster
Submetallic
Fracture
Uneven
Description
Chromium (Cr) is a hard, bluish metallic element. The only ore of chromium is the mineral chromite and 99 percent of the world’s chromite is found in southern Africa and Zimbabwe. Geologists estimate that there are about 11 billion tons of mineable chromite ore in the world, enough to supply the current demand for hundreds of years. It is mostly used for making stainless steel and other metal alloys.
Relation to Mining
While China is the leading chromium-consuming country and the leading stainless steel producer, it is not a large producer of chromite ore. The United States, Kazakhstan, India and South Africa are the largest chromite-mining countries in the world. The mining method used for extracting chromite depends greatly on the characteristics of the deposit. These characteristics include whether it is stratiform or podiform, high grade or low grade, subsurface or near surface, or massive or disseminated. Because surface mining typically is less expensive than underground mining, it is preferred, but not always possible.
Like mining, beneficiation (processing, crushing, separating, smelting, refining, etc.) for chromite depends on the characteristics of the ore deposit and on the mining methods used. For example, an operation extracting only high-grade ore may require only hand sorting and screening. Beneficiation is necessary when chromite mineral is mixed with other minerals because of geologic conditions or when mechanized mining methods are nonselective.
Uses
Chromium is alloyed (that is, mixed) with steel to make it corrosion-resistant or harder. An example is its use in the production of stainless steel, a bright, shiny steel that is strong and resistant to oxidation (rust). Stainless steel production consumes most of the chromium produced annually. Chromium is also used to make heat-resisting steel. So-called “superalloys” use chromium and have strategic military applications.
Chromium also has some use in the manufacture of certain chemicals. For example, chromium-bearing chemicals are used in the process of tanning leather. Chromium compounds are also used in the textiles industries to produce a yellow color.
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