Physical Characteristics of CHROMITE
February 6, 2009
Color is brownish black to a deep dark black.
Luster is metallic to greasy.
Transparency: Crystals are opaque.
Crystal System is isometric; 4/m bar 3 2/m
Crystal Habits include octahedrons often with dodecahedral faces modifing the edges of the octahedron to the point of rounding the crystal. Well formed crystals are rare and chromite is usually found massive or granular.
Cleavage is absent.
Fracture is conchoidal.
Hardness is 5.5
Specific Gravity is 4.5 – 4.8 (average for metallic minerals)
Streak is brown.
Other characteristics: Weakly magnetic and an octahedral parting is sometimes seen.
Best Field Indicators are crystal habit, streak, associations with ultra-basic minerals and parting
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What is Chromite?
February 6, 2009
Chromite is an iron chromium oxide mineral and the only ore of chromium metal. It is a mineral found in ultrabaisc rocks such as peridotite. It is also found in serpentines and other metamorphic rocks derived from the alteration of ultrabasic rocks. It is a high temperature mineral often found in the lower parts of magma bodies from the fractional crystallization process.
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Uses of Chromium
February 6, 2009
In metallurgy, to impart corrosion resistance, create a shiny finish, or increase hardness:
- as an alloy constituent, such as in stainless steel
- in chrome plating
- chromic acid is used in some anodizing processes
As dyes and paints:
- Chromium(III) oxide is a metal polish known as green rouge.
- Chromium salts color glass an emerald green.
- Chromium is what makes a ruby red, and therefore is used in producing synthetic rubies.
- also makes a brilliant yellow for painting
- As a catalyst.
- Chromite is used to make molds for the firing of bricks.
- Chromium salts are used in the tanning of leather.
- Potassium dichromate is a chemical reagent, used in cleaning laboratory glassware and as a titrating agent. It is also used as a mordant (i.e., a fixing agent) for dyes in fabric.
- Chromium(IV) oxide (CrO2) is used to manufacture magnetic tape, where its higher coercivity than iron oxide tapes gives better performance.
- In well drilling muds as an anti-corrosive.
- In medicine, as a dietary supplement or slimming aid, usually as chromium(III) chloride, chromium(III) picolinate, chromium(III) polynicotinate or as an amino acid chelate, such as chromium(III) D-phenylalanine.[7]
- Chromium hexacarbonyl (Cr(CO)6) is used as a gasoline additive.
- Chromium boride (CrB) is used as a high-temperature electrical conductor.
- Chromium(III) sulfate (Cr2(SO4)3) is used as a green pigment in paints, in ceramic, varnishes and inks as well as in chrome plating.
- Chromium(VI) is used in the post Ballard preparation of Gravure (rotogravure) printing Forme Cylinders. By electroplating the metal onto the second coat of copper (after the Ballard skin), the longevity of the printing cylinder is increased.
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History of Chromium Goes Back to Tarracotas
January 6, 2009
The history of chromium dates back thousands of years. Weapons found in burial pits dating from the late 3rd century BC Qin Dynasty of the Terracotta Army near Xi’an, China have been analyzed by archaeologists. Although buried more than 2,000 years ago, the ancient bronze tips of crossbow bolts and swords found at the site showed no sign of corrosion, because the bronze was coated with chromium.[2]
Crocoite (PbCrO4)
Chromium came to the attention of westerners in the 18th century. On 26 July 1761, Johann Gottlob Lehmann found an orange-red mineral in the Ural Mountains which he named Siberian red lead. Though misidentified as a lead compound with selenium and iron components, the material was lead chromate with a formula of PbCrO4, now known as the mineral crocoite.[3]
In 1770, Peter Simon Pallas visited the same site as Lehmann and found a red lead mineral that had useful properties as a pigment in paints. The use of Siberian red lead as a paint pigment developed rapidly. A bright yellow made from crocoite also became fashionable.[citation needed]
In 1797, Louis Nicolas Vauquelin received samples of crocoite ore. He produced chromium oxide (CrO3) by mixing crocoite with hydrochloric acid. In 1798, Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven.[4] He was also able to detect traces of chromium in precious gemstones, such as ruby, or emerald.[citation needed]
During the 1800s, chromium was primarily used as a component of paints and in tanning salts, but metal alloys now account for 85% of the use of chromium. The remainder is used in the chemical industry and refractory and foundry industries. Chromium is also known well for its luster when polished. It is used for decoration, etc.[citation nee
No tag for this post. Related Posts:Chrome ore producers look to China to ‘save the world’
January 2, 2009
Chrome ore prices could stage a modest recovery in the next four to six weeks on a sudden increase in enquiries from China, market participants told MB. “I am more confident about next year than I was a few weeks ago: it looks like China will save the world,” a producer source said. Enquiries from Chinese consumers and traders have picked up this week, taking ore producers…
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