Minerals crocoite

The first source of chromium was found in the mineral crocoite. Today it is obtained from the mineral chromite (FeCr O ), which is found in Cuba, Zimbabwe, South Africa, Turkey, Russia, and the Philippines. Chromite is an ordinary blackish substance that was ignored for many years. There are different grades and forms of chromium ores and compounds, based on the classification of use of the element. Most oxides of chromium are found mixed with other metals, such as iron, magnesium, or aluminum. 

Historically, chromium ore was known as Siberian red lead, which was used to make bright red paints. The source was soon identified as the mineral crocoite, and analysis indicated that it also contained lead. In 1797 the French chemist Louis-Nicolas Vauquelin (1763—1829) discovered chromium while studying some minerals that were collected in Siberia. To isolate the pure metal from its oxide, he first dissolved the lead out of the mineral with hydrochloric acid (HCl), leaving crystals of chromium oxide, which he then heated. To his surprise he ended up with crystals of pure chromium metal. 

Lead chromate (PbCrO ) is found in nature as yellow crystals in the mineral crocoite. It can be produced by reacting lead chloride and sodium dichromate. It is a popular and safe yellow pigment. 

Lead chromate occurs in nature as the minerals, crocoite and phoenic-ochroite. It is an important pigment of lead used in oil paints and water col-... 

Lead chromate is found naturally in minerals crocoite and phoenicochroite. It also is readily prepared by adding a soluble chromate such as sodium or potassium chromate to a solution of lead nitrate, lead acetate or other soluble lead(II) salt in neutral or slightly acidic solution ... 

The important valence states of chromium are II, III, and VI. Elemental chromium, chromium(O), does not occur naturally. The divalent state (II or chromous) is relatively unstable and is readily oxidized to the trivalent (III or chromic) state. Chromium compounds are stable in the trivalent state and occur in nature in this state in ores, such as ferrochromite (FeCr204). The hexavalent (VI or chromate) is the second most stable state. However, hexavalent chromium rarely occurs naturally, but is produced from anthropogenic sources (EPA 1984a). Chromium in the hexavalent state occurs naturally in the rare mineral crocoite (PbCr04) (Hurlburt 1971). 

The name and symbol come from the Greek chroma, meaning color. In 1797, Nicolas-Louis Vauquelin (1763-1829) was examining the properties of the mineral crocoite. He found that it turned vibrant colors when mixed with various chemicals. In 1798, he produced chromium metal. Chromium ores are found in a number of places, but it rarely appears in elemental form. The greatest use of chromium is for plating because it produces a hard, reflective surface that resists corrosion. It is also used as an alloy in steel, as a catalyst, and to produce emerald-green glass. 

Siberia may be said to be the birthplace of chromium as we shall see later in the 18th century the mineral crocoite, known at the time as red lead ore, was found there. Some other chromium ores had been known much earlier. And this is not surprising since chromium is one of abundant elements (0.02 per cent of the total mass of the earth s crust). But it is not easy to separate chromium even in the form of oxide and for the time being this task was beyond the power of chemists. Although chromium compounds have different colours, this peculiar fact did not attract the attention of scientists to chromium minerals. 

The most important ore of chromium is chromite, FeCr204- The element was not known to the ancients, but was discovered in 1798 in lead chromate, PbCr04, which occurs in nature as the mineral crocoite. 

Red ore of lead is sometimes used for the lead chromate mineral crocoite. As noted by FitzHugh (1986), Forbes and Petrie have suggested that natural minium was the source of the pigment of... 

Chromium was first isolated and identified as a metal in 1789 by Vauquelin who was working with a rare mineral, Siberian red lead or crocoite [14654-05-08] PbCrO (3). The name chromium comes from the Greek word chroma color and resulted from the wide variety of brilliant colors... 

The first chromium compound was discovered in the Ural mountains of Russia, during the latter half of the eighteenth century. Crocoite [14654-05-8] a natural lead chromate, found immediate and popular use as a pigment because of its beautihil, permanent orange-red color. However, this mineral was very rare, and just before the end of the same century, chromite was identified as a chrome bearing mineral and became the primary source of chromium [7440 7-3] and its compounds (1) (see Chromiumand chromium alloys). 

Finally, in 1797, the Frenchman L. N. Vauquelin discovered the oxide of a new element in a Siberian mineral, now known as crocoite (PbCr04), and in the following year isolated the metal itself by charcoal reduction. This was subsequently named chromium (Greek xpco ia, chroma, colour) because of the variety of colours found in its compounds. Since their discoveries the metals and their compounds have become vitally important in many industries and, as one of the biologically active transition elements, molybdenum has been the subject of a great deal of attention in recent years, especially in the field of nitrogen fixation (p. 1035). 

Occurrence. The ore of Cr of higher commercial importance is chromite (FeCr204). Other minerals are crocoite PbCr04 and chrome ochre Cr203. About 2% Cr in emerald Be3Al2Si6018 is the source of its green colour. Chromium is comparable in abundance in the earth s crustal rocks with V and Cl. 

Chromium occurs in the minerals chromite, Fe0 Cr203 and crocoite, PbCr04. The element is never found free in nature. Its abundance in earth s crust is estimated in the range 0.01% and its concentration in sea water is 0.3 qg/L. The element was discovered by Vaquelin in 1797. 

In 1799 Citizen Tassaert, a Prussian chemist who had been working for several years at the School of Mines of Paris, discovered chromium in an iron mineral found at the Carrade Villa near Gassin in the department of du Var. He too regarded the mineral as a chromate of iron (89). Since chromium had previously been detected in the red lead of Siberia (crocoite), in the emerald, and in the ruby, the chrome-iron mineral... 

P. S. Pallas describes the red lead of Siberia (crocoite), in which Vauquelin later discovered chromium. This mineral had been analyzed four years earlier by J. G. Lehmann. 

Chromates are a small group of minerals that contain the simple Cr04 molecule. Crocoite is the most common species in this group, a bright orange compound that is sometimes used as a pigment. 

Lead chromate occurs in nature as crocoite, an orange-red mineral. Synthetically prepared lead chromate and its solid solutions with lead sulfate and lead molybdate represent a hue range from primrose yellow to red. The various hues of chrome yellow, chrome orange, and molybdate orange depend not only on composition but also on crystal structure and particle size. 

Early History.— Tehmann, writing in 1762 to de Bufton, described a new mineral from Siberia, now known as crocoite q.v.). On examination of this mineral by Vauquelin and Macquart in 1789, lead, iron,... 

Chromium as a metallic element was first discovered two hundred years ago, in 1797. But the history of chromium really began several decades before this. In 1761, in the Beresof Mines of the Ural Mountains Johann Gottlob Lehmann obtained samples of an orange-red mineral, which he called Siberian red lead . He analyzed this mineral in 1766 and discovered that it contained lead mineralised with a selenitic spar and iron particles. The mineral he found was crocoite, a lead chromate (PbCr04). 

He described it as a very remarkable red lead mineral which has never been found in any other mine. When pulverised, it gives a handsome yellow guhr which could be used in miniature painting. Chromium from the Beresof Mines and Siberia was used as a paint pigment. Due to its rarity, this later became a collector s item and increased in popularity in the paint industry. A bright yellow made from crocoite fast became the fashionable color for the carriages of the nobility in both France and England. 

Chromium was first identified in 1797 by the French chemist Louis-Nicolas Vauquelin, who isolated it from crocoite, a mineral also called Siberian red lead. The name for chromium is taken from the Greek chroma, which means color. This is a fitting name, because chromium compounds are often found in vividly colorful shades of green, red, or yellow. As such, chromium compounds historically have found extensive use as pigments for paints. In contrast, elemental chromium is a shiny, hard, yet brittle, steel-gray metal. Since chromium is not found naturally in its free elemental state, it is usually extracted from chromite, FeCr204. 

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