Malachite A mineral is a naturally occuring, homogeneous, solid with a crystalline atomic structure. Crystallinity implies that a mineral has a definite and limited range of composition, and that the composition is expressible as a chemical formula. Some definitions of minerals give them as inorganic materials, however both diamonds and graphite are considered minerals, and both are primarily comprised of carbon, which would make them organic. So this leads me, as an engineer, to believe that mineralogists do not have a good, precise definition of a mineral, but rather a loose definition. The definition above, is the most inclusive and would include all substances currently described as minerals. The key items that make something a mineral are occurring naturally, and the definite crystal structure, that is expressible as a chemical formula. Rocks that do not meet this criteria are referred to as amorphis - not having a definite structure or expressible as a chemical formula. Some elements that occur naturally and are minerals are arsenic, bismuth, platinum, gold, silver, copper, and sulphur.

THE DEFINITION OF ORGANIC: Organic chemistry is the study of those substances containing carbon in combination with hydrogen (H), and a few other non metals, namely oxygen (O), nitrogen (N), sulfur (S) and the halogens (F2, Cl2, Br2, and I2). Malachite is a copper bearing mineral, with as much as 58% copper content. The distinctive bright-green hydrous CARBONATE MINERAL malachite is a common but minor ore of copper. It is usually found in copper deposits associated with LIMESTONE, occurring with AZURITE as the weathering product of other copper ore minerals. Hardness is 3 1/2 to 4, streak is pale green, specific gravity is 3.9 to 4.1, and luster is adamantine to silky. Malachite forms needlelike prismatic crystals (monoclinic system) that are rarely distinct; it is usually found in granular, earthy, or fibrous masses and rounded, banded crusts. Malachite is used as a decorative stone when cut and polished, a semiprecious gem, and a green pigment.

Half of the world's copper deposits are in the form of chalcopyrite ore. All important copper-bearing ores fall into two main classes: oxidized ores and sulfide ores. Sulfide ores are more important commercially. Ores are removed either by open-pit or by underground mining. Ores containing as little as 0.4% copper can be mined profitably in open-pit mining, but underground mining is profitable only if an ore contains 0.7%-6% copper. The oxidized ores, such as cuprite and tenorite, can be reduced directly to metallic copper by heating with carbon in a furnace, but the sulfide ores, such as chalcopyrite and chalcocite, require a more complex treatment in which low-grade ores have to be enriched before smelting begins. This involves the ore-flotation process, in which the ore is crushed and powdered before it is agitated with water containing a foaming agent and an agent to make the copper-bearing particles water-repellent.

These particles accumulate in the froth on the surface of the flotation tank, and this froth is skimmed off and heated to about 800 deg C to remove some of the water as well as antimony, arsenic, and sulfur, which are also present. Malachite: Malachite mineral information and data. 3½ - 4 Name: Named in antiquity (see Pliny the Elder, 79 CE) molochitus after the Greek μαλαχή, "mallows," in allusion to the green color of the leaves. Known in the new spelling, malachites, at least by 1661. Malachite is a green, very common secondary copper mineral with a widely variable habit. Typically it is found as crystalline aggregates or crusts, often banded in appearence, like agates. It is also often found as botryoidal clusters of radiating crystals, and as mammillary aggregates as well. Single crystals and clusters of distinguishable crystals are uncommon, but when found they are typically acicular to prismatic. It is also frequently found as a pseudomorph after Azurite crystals, which are generally more tabular in shape.

The Cu analogue of chukanovite . Structurally related to the Rosasite Group . Malachite: Uses and properties of the mineral and gemstone Home » Minerals » Malachite Malachite Used as an ore of copper, a pigment, a gemstone, and a sculptural material for thousands of years. Malachite Gemstones: A malachite cabochon (30x40 millimeter) and a malachite puffed heart, both cut from rough mined in the Democratic Republic of the Congo. This oval cabochon shows the agate-like banding in various shades of green that is typical of malachite. The puffed heart shows concentric structures. What is Malachite? Malachite is a green copper carbonate hydroxide mineral with a chemical composition of Cu2(CO3)(OH)2. It was one of the first ores used to produce copper metal. It is of minor importance today as an ore of copper because it is usually found in small quantities and can be sold for higher prices for other types of use. Malachite has been used as a gemstone and sculptural material for thousands of years and is still popular today.

Today it is most often cut into cabochons or beads for jewelry use. Malachite has a green color that does not fade over time or when exposed to light. Those properties, along with its ability to be easily ground to a powder, made malachite a preferred pigment and coloring agent for thousands of years. Botryoidal Malachite: Close-up of botryoidal malachite in a seafoam green color from Bisbee, Arizona. This view spans an area of the specimen about 5 millimeters wide and high. Specimen and photo by Arkenstone / . Where Does Malachite Form? Malachite is a mineral that forms at shallow depths within the Earth, in the oxidizing zone above copper deposits. It precipitates from descending solutions in fractures, caverns, cavities, and the intergranular spaces of porous rock. It often forms within limestone where a subsurface chemical environment favorable for the formation of carbonate minerals can occur. Associated minerals include azurite , bornite , calcite , chalcopyrite , copper , cuprite , and a variety of iron oxides. Some of the first malachite deposits to be exploited were located in Egypt and Israel.

Over 4000 years ago, they were mined and used to produce copper. Material from these deposits was also used to produce gemstones, sculptures, and pigments. Several large deposits in the Ural Mountains of Russia were aggressively mined, and they supplied abundant gem and sculptural material in the 1800s. Very little is produced from these deposits today. Much of the malachite entering the lapidary market today is from deposits in the Democratic Republic of the Congo. Smaller amounts are produced in Australia, France, and Arizona. Stalactitic malachite: A specimen of stalactitic malachite from the Kasompi Mine, Democratic Republic of the Congo. The specimen is approximately 21 x 16 x 12 centimeters in size. Specimen and photo by Arkenstone / . Physical Properties of Malachite A minor ore of copper. Gemstones, small sculptures, pigment. Physical Properties of Malachite Malachite's most striking physical property is its green color. All specimens of the mineral are green and range from a pastel green, to a bright green, to an extremely dark green that is almost black.

It is typically found as stalactites and botryoidal coatings on the surfaces of underground cavities - similar to the deposits of calcite found in caves. When these materials are cut into slabs and pieces, the sawn surfaces often exhibit banding and eyes that are similar to agate . Malachite is rarely found as a crystal, but when found, the crystals are usually acicular to tabular in shape. The crystals are bright green in color, translucent, with a vitreous to adamantine luster. Non-crystalline specimens are opaque, usually with a dull to earthy luster. Malachite is a copper mineral, and that gives malachite a high specific gravity that ranges from 3.6 to 4.0. This property is so striking for a green mineral that malachite is easy to identify. Malachite is one of a small number of green minerals that produces effervescence in contact with cold, dilute hydrochloric acid . It is also a soft mineral with a Mohs hardness of 3.5 to 4.0. Painting with Malachite: Pietro Perugino (c.

1446-1523) used malachite pigment when painting the green garment colors in his Nativity (c. 1503). He used "Verona green earth" pigment for the grass. The deeper green color of malachite gave the garments a contrasting and more vivid appearance. The best way to learn about minerals is to study with a collection of small specimens that you can handle, examine, and observe their properties. Inexpensive mineral collections are available in the Geology.com Store . Malachite Pigment: A photograph looking down into a jar of malachite pigment. This pigment was produced from malachite mined near the city of Nizhniy Tagil, in the Ural Mountains of Russia. It has a particle size of 20 microns. We obtained this pigment from NaturalPigments.com. Malachite as a Pigment Malachite has been used as a pigment for thousands of years. It was one of the oldest known green pigments to be used in paintings.

The mineral malachite is an excellent material for producing a powdered pigment because it can easily be ground into a fine powder, it mixes easily with vehicles, and it retains its color well when exposed to light over time. Alternative names for malachite pigment include copper green, Bremen green, Olympian green, green verditer, green bice, Hungarian green, mountain green, and iris green. Malachite pigment is found in the paintings of Egyptian tombs and in paintings produced throughout Europe during the 15th and 16th centuries. Its use declined significantly in the 17th century as alternative green colors were developed. Today, malachite pigment is sold by a few manufacturers who specialize in providing materials to painters who practice historically accurate techniques. Azurmalachite: Cabochons of azurmalachite showing nice patterns of azurite (blue) and malachite (green). They were cut from material produced at the Morenci Mine in Arizona. These cabs were cut from thin vein material and have a natural wall-rock backing. Both cabs are about 25 millimeters tall.

Banded Malachite: Two views of a specimen of botryoidal malachite - one external and one internal polished surface. This photo pair shows how agate-like bands and eyes of malachite occur beneath a botryoidal structure. This specimen was collected near Katanga, Democratic Republic of the Congo. Photograph by Didier Descouens. Used here under a Creative Commons License . Malachite as a Gem Material The vivid green color, bright polished luster, banding and eyes of malachite make it very popular as a gemstone. It is cut into cabochons , used to produce beads, sliced into inlay material, sculpted into ornamental objects, and used to manufacture tumbled stones . Small boxes made from slices of malachite are attractive and popular. Some of the most spectacular gem-quality malachite involves intergrowths, inclusions, and admixtures of malachite with other copper minerals such as azurite ( azurmalachite ), chrysocolla, turquoise , and pseudomalachite (eilat stone). Malachite's use as gem and ornamental stone is limited by its properties.

It has perfect cleavage and a Mohs hardness of 3.5 to 4. These limit its use to items that will not suffer abrasion and impact. It is also sensitive to heat and reacts with weak acids. These properties further limit its use and require care during cleaning, repair, and maintenance. Malachite is sometimes treated with wax to fill small voids and improve its luster. Synthetic malachite has been produced and used to make jewelry and small sculptures. Poorly done synthetics are often recognized by their unnatural color. The better synthetics can usually be recognized because their banding and eyes do not have a natural geometry. An experienced person can identify most of the synthetic and imitation materials on sight. More Minerals Malachite: The mineral malachite information and pictures Advertising Information The Mineral malachite Malachite is a popular mineral with its intense green color and beautiful banded masses. The banded specimens are formed by massive , botryoidal , reniform , and especially stalactitic Malachite that are dense intergrowths of tiny, fibrous needles. Dense banded specimens are often sliced and polished to bring out their beautiful coloring.

The bands may consist of concentric rings with interesting patterns; such specimens are highly sought after. These concentric banded specimens are most commonly from African sources. Polished, banded Malachite has been carved into ornaments and worn as jewelry for thousands of years, and in some ancient civilizations it was thought to be a protection from evil when worn as jewelry. Malachite is generally found together with blue Azurite , and sometimes the two may occur admixed or banded together, forming what is commonly known in the gem and mineral trade as " Azure-Malachite ". Malachite may also replace Azurite crystals, retaining the original Azurite shape but chemically alter ing it. For additional information, see the gemstone section on Malachite . USES When found in large pieces, the banded variety of Malachite makes a precious ornamental stone. Small ornamental objects, such as boxes and animal figures, are carved out of this compact stone, and if properly polished, they can be valuable. Malachite is also used as a minor gemstone, and is cut into cabochon s and fashioned into necklace beads.

"Azure-malachite" is also used as gemstone and has the same gem applications as banded Malachite. Malachite is very popular among mineral collectors, especially interestingly shaped and banded specimens. It is also used as an ore of copper and crushed to make a green pigment. NOTEWORTHY LOCALITIES There are many places where fine Malachite comes from. Only the best will be mentioned here. Much of the original gem material, from which ornaments and jewelry were made since early times, was from the large deposits in Yekaterinburg Oblast in the Ural Mountains of Russia. Africa contains several outstanding Malachite deposits. The mines at Katanga (Shaba), especially at Kolwezi, in the D.R. Congo (Zaire) produce Malachite in all sorts of odd shapes and forms, and are the source of the best banded , concentric , stalactitic and sparkling specimens. Tsumeb, Namibia, has also produced some of the best Malachite, especially Malachite pseudomorph s after Azurite . The Emke Mine in Ogonja, Namibia is also an outstanding Malachite locality.

Morocco also contains fabulous Malachite sources, specifically in Touissit and Kerrouchene. Australia contains important Malachite localities at Burra Burra, South Australia; the Rum Jungle, Batchelor, Northern Territory; and the Sir Dominick Mine, Flinders Ranges, South Australia. A new specimen producer is China, where gorgeous Malachite comes from the Shilu Mine, Yangchun, Guangdong Province, with amazing stalactite s worthy of special mention. Chessy, in the Rhône-Alpes, France, is an old and classic locality, where excellent pseudomorph s of Malachite after Cuprite occur in octahedral and even dodecahedral crystals. Malachite from Brazil is especially prolific in Seabra, Bahia; and popular Mexican Malachite deposits include El Cobre, Concepcion del Oro, Zacatecas; and the now popular Milpillas Mine, Cananea, in Sonora. In the U.S., Arizona is by far the most prolific producer of Malachite, and the mines at Bisbee, Cochise Co., are well known among all collectors for their outstanding variety and quality of Malachite.

Other important Arizona localities are Morenci, Greenlee Co.; Ajo, Pima Co.; Mammoth-Saint Anthony, Tiger, Pinal Co.; and the Globe-Miami District, Gila Co. PHOTO OF THE MINERAL MALACHITE, (Cu2(CO3)(OH)2, Copper Carbonate Hydroxide) A COPPER BEARING MINERAL WITH AS MUCH AS 50% COPPER, WHICH IS WHERE IT GETS ITS GREEN COLOR. The distinctive bright-green hydrous CARBONATE MINERAL malachite is a common but minor ore of copper. It is usually found in copper deposits associated with LIMESTONE, occurring with AZURITE as the weathering product of other copper ore minerals. Hardness is 3 1/2 to 4, streak is pale green, specific gravity is 3.9 to 4.1, and luster is adamantine to silky. Malachite forms needlelike prismatic crystals (monoclinic system) that are rarely distinct; it is usually found in granular, earthy, or fibrous masses and rounded, banded crusts.

Malachite is used as a decorative stone when cut and polished, a semiprecious gem, and a green pigment. The chemical element copper is a reddish metal at the head of group IB in the periodic table. Its symbol is Cu; atomic number, 29; and atomic weight, 63.546. Copper follows the first transitional series of elements. Copper was the first metal used by humans and is second only to iron in its utility through the ages. The name is derived from the Latin cuprum, copper, from the earlier Latin Cyprium, Cyprian metal. The discovery of the metal dates from prehistoric times, and it is estimated that copper was first used about 5000 BC or even earlier. Natural Occurrence and Extraction In Roman times much of the copper was obtained from the island of Cyprus, as the name implies. Copper today is mined in many parts of the world, the largest producers at present being Chile, Peru, Poland, the United States, Zaire, and Zambia. More than 160 minerals containing copper are known.

Copper constitutes 70 parts per million of the Earth's crust and is present to the extent of 0.020-0.001 parts per million in seawater. Copper in its native state--such as that found in the Lake Superior region of North America--is often so pure that it requires only melting with a flux to produce "lake copper," which for many years was the world standard for pure copper. About 80% of all copper mined today, however, is derived from low-grade ores containing 2% or less of the element. Half of the world's copper deposits are in the form of chalcopyrite ore. All important copper-bearing ores fall into two main classes: oxidized ores and sulfide ores. Sulfide ores are more important commercially. Ores are removed either by open-pit or by underground mining. Ores containing as little as 0.4% copper can be mined profitably in open-pit mining, but underground mining is profitable only if an ore contains 0.7%-6% copper.

The oxidized ores, such as cuprite and tenorite, can be reduced directly to metallic copper by heating with carbon in a furnace, but the sulfide ores, such as chalcopyrite and chalcocite, require a more complex treatment in which low-grade ores have to be enriched before smelting begins. This involves the ore-flotation process, in which the ore is crushed and powdered before it is agitated with water containing a foaming agent and an agent to make the copper-bearing particles water-repellent. These particles accumulate in the froth on the surface of the flotation tank, and this froth is skimmed off and heated to about 800 deg C to remove some of the water as well as antimony, arsenic, and sulfur, which are also present. The residue is then mixed with silica and melted in a furnace at 1,400 deg-1,500 deg C. This produces two liquid layers: a lower layer of copper matte (cuprous sulfide mixed with iron sulfide and oxides), and an upper layer of silicate slag, which is drawn off.

Silica or siliceous copper ore is added to the liquid matte in a converter, and air under pressure is blown through the liquid. Upon removal of the iron slag, the copper(I) sulfide that remains is reduced to copper by heating in a controlled amount of air. The remaining molten copper, which is 98%-99% pure, is either cast into blocks of blister copper or into anodes. The final stage of purification is mainly by electrolytic refining, which yields copper of 99.95%-99.97% purity. The impure copper is made the anode of an electrolytic cell that contains pure strips of copper as the cathode and an electrolyte of aqueous copper(II) sulfate. During electrolysis, copper is transferred from the anode to the cathode. An anode sludge containing silver and gold is produced during this process, and this increases its economic feasibility. Physical and Chemical Properties Eleven isotopes of copper are known, two of which are not radioactive and occur with a natural abundance of 69.09% and 30.91%, respectively.

Copper melts at 1,083.4 deg plus or minus 0.2 deg C (in a vacuum), boils at 2,567 deg C, and has a density of 8.96 at 20 deg C. The element has a hardness of 3, takes on a bright metallic luster, has a cubic crystal structure, and is malleable, ductile, and a good conductor of heat and electricity, second only to silver in electrical conductivity. The outstanding feature of copper and the other metals of Group IB (gold and silver) is their resistance to chemical attack. Copper is slowly attacked by moist air, and its surface gradually becomes covered with the characteristic green patina that consists of basic sulfate. At about 300 deg C copper is attacked by air or oxygen, and a black coating of copper(II) oxide forms at the surface; at a temperature of 1,000 deg C copper(I) oxide is formed instead. The metal is attacked by sulfur vapor, with the formation of copper(I) sulfide; and by the halogens, which form copper(II) halides, except iodine, which forms copper(I) iodide.

Copper is not attacked by water or steam, and dilute nonoxidizing acids, such as dilute hydrochloric and dilute sulfuric acids, have no effect in the absence of an oxidizing agent. The metal is attacked by boiling concentrated hydrochloric acid with the evolution of hydrogen, by hot concentrated sulfuric acid, and by dilute or concentrated nitric acid. Alloys of Copper Copper mixes well with many elements, and more than 1,000 different alloys have been formed, several of which are technologically significant. The presence of the other element or elements can modify the hot or cold machining properties, tensile strength, corrosion fatigue, and wear resistance of the copper; it is also possible to create alloys of pleasing colors. The best-known alloy of copper is BRASS, which consists of copper containing between 5% and 40% zinc. It possesses a high tensile strength, hardness, and wear-resistance. The addition of 0.5%-3% lead to a brass alloy (leaded brass) improves the machinability of brass, and brass containing 30%-40% zinc and 1% tin (tin brass) has a high corrosion-resistance.

Another useful alloy of copper is nickel silver, which consists of copper (55%-65%), nickel (10%-18%), and zinc (17%-27%). It is used as a base for silver-plating items such as costume jewelry and tableware. Phosphor bronze is formed by the addition of up to 0.35% of phosphorus to copper-tin alloys containing up to 10% tin. This alloy has great resiliency, fatigue endurance, hardness, and corrosion resistance; these properties make it suitable for use in springs and diaphragms. Silicon bronze, consisting of 1%-3% silicon, 95%-96% copper, and small amounts of other metals--for example lead, tin, zinc, manganese, iron, or nickel--is as strong as mild steel and has a high resistance to corrosion. It is used in the production of equipment for chemical plants in which corrosive liquids are handled. Aluminum-copper bronzes contain aluminum (5%-12%) and sometimes zinc and silicon; they are also corrosion resistant, and have good strength, hardness, and wear resistance. They are used for carrying corrosive liquids such as hot brine in salt refineries.

Beryllium-copper alloys, containing 2% beryllium, have a high corrosion resistance and high tensile strength, with considerable fatigue and wear resistance. They find wide application where high strength is required and for making non-spark-forming tools. Copper is a trace element essential to the healthy life of many plants and animals, in which it usually occurs as part of the oxidizing enzymes such as ascorbic acid oxidase, tyrosinase, lactase, and monoamine oxidase. These enzymes, which are high-molecular-weight proteins containing 0.05%-0.35% of Cu, play an important part in living oxidation and reduction reactions, in which the copper undergoes cyclic changes between Cu(I) and Cu(II) oxidation states. The metal is tightly bound to ligand sites, containing oxygen, sulfur, or nitrogen atoms on the protein. The normal diet of humans includes between 2 and 5 mg of copper per day, exceeding the body maintenance requirements of about 2 mg per day. The hereditary deficiency of the protein ceruloplasmin, known as Wilson's disease, is associated with a pathological increase in the copper content of almost all tissues, particularly the brain and liver.

Albino mammals lack the normal form of the copper-containing enzyme tyrosinase, which participates in the synthesis of the pigment melanin. Copper can be toxic in large quantities, especially to lower organisms such as bacilli, fungi, and algae. Applications of Copper and Its Compounds The electrical industry is a major consumer of copper. The metal is used for the windings of generators and for conveying electrical power. Its resistance to chemical attack and its high thermal conductivity make copper a useful metal for condensers in chemical plants and for car radiators. Copper tubing is widely employed in plumbing, and finely divided copper is used as an industrial catalyst in the oxidation of methanol to formaldehyde. Copper compounds, such as Fehling solution, are used in analytical tests for sugars. Copper(II) sulfate has many industrial applications, including the preparation of Bordeaux mixture (a fungicide) and the manufacture of other copper compounds. It is also used in electroplating solutions, in textile dyeing, and as a timber preservative. Copper wire for electric and electronic uses was the most important area of refined copper sales. Brass products, industrial machinery, automobiles and other forms of transport, and consumer products were all large copper consumers.

In the fields where copper traditionally has been strong, only housing failed to revive. Solvent extraction, a new copper refining technique, is proving highly successful. In a process resembling that recently developed for treating gold ores, low-grade copper ores--once considered valueless--are treated with a weak acid solution, and after being combined with other chemicals, the leachate is subjected to electrolysis. Copper derived from leachates is called "electrowon," and costs for electrowon copper are far below those for copper derived from smelting. THE ORE AT LEFT IS THE MINERAL REALGAR, COMPOSED OF THE ELEMENTS OF ARSENIC AND SULFUR. IT IS A MAJOR SOURCE OF ARSENIC Arsenic is a metallic chemical element in Group VA of the periodic table. Its symbol is As, its atomic number 33, and its atomic weight 74.9216. The Earth's crust contains only about 5.5 parts arsenic per million. Arsenic occurs in numerous minerals, in particular realgar, orpiment, and arsenopyrite. Arsenic and some arsenic compounds have been known for a long time.

Aristotle thought that arsenic was a kind of sulfur. In about 1250, Albertus Magnus became the first to describe a method of manufacturing arsenic. Since then the method has scarcely changed: the mineral arsenopyrite is heated and decomposes with the liberation of arsenic gas. The gas can be condensed on a cold surface. Arsenic exists in three allotropic modifications: the yellow (alpha); the black (beta); and the metallic, or gray (gamma). Normally arsenic is found in its metallic form, which is the most stable and at normal pressure does not melt but sublimes at about 615 degrees C. It forms alloys with other metals. The alpha and beta modifications have no metallic properties. Arsenic is fairly reactive. Above 400 degrees C it burns with a bluish flame, forming arsenic trioxide. This compound is known as white arsenic and is used as a rat poison. Arsenic was used in Aristotle's time to harden copper. Orpiment and realgar have long been used as depilatories in the leather industry. When orpiment is rubbed on silver, it gives the surface a golden color.

Orpiment thus appears to have one of the properties attributed to the philosophers' stone, and it was therefore an important material for alchemists. The toxic quality of arsenic also has been known since ancient times. In the human body it accumulates in the nails and the hair, where it can be detected--even in the bodies of persons long dead--by the atomic absorption method. The acute symptoms are diarrhea and cramps. In cases of chronic poisoning, anemia and paralysis may appear. If there is prolonged contact with the skin, malignant skin tumors can develop. BAL (British Anti-Lewisite) was developed as an antidote against the arsenic-containing war gas Lewisite, but it also proved useful in treating common arsenic poisoning. In medicine, 4-aminobenzene arsenic and 4-hydroxybenzene arsenic compounds are used in certain infections. The best known is Salvarsan, an antisyphilis drug. Commercially, arsenic is added to lead to harden it and is used in the production of herbicides and pesticides. THE PHOTO AT LEFT IS SILVER.

SILVER IS USED IN PHOTOGRAPHY (PRIMARY USE), COINAGE, MIRRORS, ELECTRONIC CIRCUITS, SWITCHES, SOLDERS, BATTERIES, BEARINGS, AND SILVER IODIDE IS USED TO PRODUCE RAIN BY SEEDING THE CLOUDS. THE ELEMENTS OF SILVER, GOLD, AND COPPER ARE OFTEN FOUND IN NATURE TOGETHER OCCURING IN THE SAME DEPOSIT. Silver is a heavy metallic element with a brilliant white luster. The chemical symbol for silver, Ag, derives from its Latin name, argentum, meaning "white and shining"--an apt description. The metal has been used as currency since ancient times, both in the mass (bullion) and in the form of coins. Silver shares Group IB of the periodic table with gold and copper. Silver, gold, platinum, and mercury are together categorized as noble metals because they do not oxidize readily when heated, nor do they dissolve in most of the inorganic acids. Because of silver's value it is also categorized as a precious metal, as are gold, platinum, iridium, and palladium.

Besides being a monetary metal, silver has also long been used for making jewelry, solid silver or silver-plated objects such as eating utensils, and other tokens of wealth because of its beauty. Only about 6% of the world production of silver goes to coinage, and only about 10% to jewelry, silver plate, and sterling ware. By contrast, more than 40% of all silver produced is used in photography because of light-sensitive properties of silver compounds. Thus photographic film is composed of an acetate upon which a thin gelatin layer, the emulsion, is spread. The emulsion contains a silver salt, a halide, as well as organic and inorganic sensitizing compounds. Silver iodide is used for fast films, silver bromide for slower films and fast-printing papers, and silver chloride for most printing papers. When light falls upon them the silver compounds are photooxidized. That is, electrons are released from the halide ions and combine with the silver ions, forming elemental silver atoms suspended in the gelatin emulsion. Placing the film in a developer continues the oxidation process in the salt crystals already affected by light but has no effect on unaffected crystals.

Thereafter the film is in a sodium thiosulfate bath to halt the oxidation process, leaving a negative image from which a positive print can be made. Color films also employ dyes. The rest of the silver produced goes into various industrial and medical applications and into the silvering of mirrors. Silver's exceedingly high electrical conductance and resistance to oxidation make it valuable in critical electrical contacts, switches, printed circuits, solders, long-lasting batteries, and many forms of electrical and electronic equipment. It is used in bearing alloys for airplanes and diesel engines and in some automobiles as well, and, alloyed with copper, it is used for welding. In colloidal form it serves as a catalyst in the manufacture of certain alcohols. Alloyed with cesium, it is employed in photocells. Finally, in the form of silver iodide, it is used to seed clouds for WEATHER MODIFICATION purposes. Occurrence of Silver is a relatively rare element, ranking about 65th in cosmic abundance and about 68th in abundance in the Earth's crust.

It is found in small quantities in many locations on Earth, sometimes in relatively pure native form but more often in silver sulfide--Ag(2)S--ores (see ARGENTITE), in other ores such as cerargyrite, or horn silver (silver chloride, AgCl), and as a minor constituent in ores of copper, lead, and zinc. It is also found in minute quantities in seawater. Silver is sufficiently widespread as a native metal for the Egyptians to have used it without complex refining processes before 3500 BC. Historically, however, the most important mines have been those that were discovered by the Spaniards in Central and South America during the 16th century AD, as well as the U.S. COMSTOCK LODE discovered in Nevada in 1859 and the deposits in the Coeur d'Alene area of Idaho. Next to gold, it is the most malleable and ductile metal known. It is harder than gold but softer than copper. This softness limits its use, even for coinage, unless it is alloyed with about 10% copper. When alloyed with 7.5% copper, it is known as sterling silver.

As a pure element it can absorb oxygen in the amount of 20 times its own volume at its melting point of 960.8 deg C (1,761.4 deg F). The boiling point of the metal is 2,210 deg C (4,010 deg F). Silver's atomic number is 47, and its atomic weight is 107.868. Naturally occurring silver consists of two stable isotopes: silver-107 (51.82%) and silver-109 (48.18%). Crystals of silver have a face-centered cubic lattice structure The CYANIDE PROCESS is generally the extractive method of choice. It can also be used to reclaim silver from zinc ores after the volatile zinc has been distilled from them. In this process a dilute sodium cyanide solution is used to dissolve the silver in the presence of air. This yields a silver cyanide complex that, after removal from the unreacted ore, is treated with zinc dust to recover elemental silver. The cyanide process, which appeared about 1859, was responsible for the recovery of the silver of the Comstock Lode.

By 1910 the so-called froth process of concentrating silver ores became common, and today it accounts for about 75% of all silver recovered. The ore is ground to a powder, placed in large vats containing water suspensions of frothing agents, and thoroughly agitated by jets of air. Depending on the agent used, either the silver-bearing ore or the useless residues adhere to the bubbles of the froth and are skimmed off. The final refining is electrolytic. Silver is also recovered from used photographic film by burning the film and chemically treating the ashes as if they were copper ore. Unfortunately, less than 20% of all silver used for film is recovered. The remainder is irrecoverable by any practical method. Silver as a Monetary Metal By at least the 8th century BC it is likely that all countries of the ancient Middle East were using both silver and gold as currency. This practice is called bimetallism when a fixed ratio is set between the values of the two forms of coins. In the United States, bimetallism was officially adopted in 1792.

The gold discoveries of the mid-19th century thereafter led to lower gold and higher silver prices, silver eventually being sold in the market for higher values than it held at the mint. As a result, a prohibition was placed on silver coinage in the United States in 1873. Later discoveries of silver in the western states changed the picture again. In the late 19th century the metal became involved in a contest between tight money adherents and the FREE SILVER advocates--farmers, debtors, and silver-mine owners who advocated a return to bimetallism, thereby increasing the supply of money in circulation. In 1900, Congress officially adopted a single gold-based monetary standard. In the 1960s the Treasury Department ceased issuing silver certificates, the paper money secured by silver. By 1970, when the silver content of the half dollar was reduced to nothing, the silver content of all regular coinage had been eliminated entirely.

Copper, Azurite, Malachite, Rhodocrosite, Chrysocolla Rhodocrosite Top My small collection of minerals contains five species, all of which were removed from the copper mines of Butte, Montanna during the 1950's. Of these five species, native copper, the copper carbonates azurite and malachite, and the amorphous copper silicate chrysocolla are copper-bearing substances. Rhodocrosite ( MnCO2 ) is, like azurite and malachite, a carbonate mineral. However, rhodocrosite is an ore of manganese rather than copper. Copper ( Cu ) is a native metal which has long been utilized by humans as a natural resource. The crystalline lattice of this mineral contains only elemental copper and its structure is derived from metallic bonds. Like all metals, native copper is dense, soft, malleable, and ductile. It conducts well. It is opaque and demonstrates the shiny, highly reflective luster typical of metals. In color it is the familiar, rosy copper red; it possesses a red streak. Exposed surfaces may tarnish to black oxide or green carbonate.

Native copper possesses a face-centered cubic lattice, which is the most dense and symmetric of all possible crystalline structures. It is of the isometric or cubic crystal system. Individual copper crystals may may be of cubic, dodecahedral, tetrahedral, and very rarely of octahedral shape. Aggregates of crystals may be wiry in habit or form a dendritic, arborescent branching structure. Mineral specimens demonstrating whole individual crystals and well-formed crystal faces are relatively rare. The two minerals azurite ( ), and the copper cation ( Cu2+ ). Azurite is royal blue or brilliant blue in color while malachite may be bright to dark green. The coloration in both species is idiochromatic and is due to the presence of copper, which is a chromophore and possesses a strong pigmenting effect. Malachite's green results from the fact that the copper which it contains is more highly oxidized than that of azurite. Aggregates of crystals of both species are frequently botryoidal or mammillary in habit. Large individual crystals of malachite are rare. More commonly the mineral occurs in rings, bands, and concentric layers composed of varying shades of green.

Both azurite and malachite occur as earthy, incrusted masses. Rhodocrosite ( MnCO3 ) is member of the carbonate class and an ore of manganese. Its characteristic rose pink or red color is idiochromatic and is due to the presence of the chromophore manganese ( Mn ). Rhodocrosite is translucent and will transmit light diffusely; it possesses a vitreous or pearly luster. Like azurite and malachite, rhodocrosite is a member of the carbonate class. However, rhodocrosite contains neither water ( H2O ) nor the hydroxyl anion ( OH- ) and is therefore not a hydrous carbonate. Instead it is a member of the calcite group. Rhodocrosite is like all calcite minerals a member of the rhombohedral crystal system. Rhodocrosite's cleavage is perfect in three directions and provides external indication of its rhombohedral internal structure. Crystals are rare but may be rhombohedral in shape; more typically the mineral demonstrates botryoidal, encrusting habit.

The hydrous silicate chrysocolla ( Cu2H2Si2O5(OH)4 ) is an ore of copper. Chrysocolla is a hydrous or basic copper silicate because it contains the hydroxyl anion ( OH- ). This species is not a true mineral and does not possess a crystalline lattice. Instead, it is an amorphous 'silica gel' or gelatinous precipitate. It is, however, a copper-bearing solid substance which is commonly found in association with minerals such as azurite, malachite, and native copper. In color chrysocolla is green to sky-blue. This coloration is idiochromatic and is due to the presence of the chromophore copper ( Cu ). Chrysocolla is translucent; samples may be of vitreous or glassy luster or appear greasy, dull, or earthy. It is very brittle, sometimes fragile; it has no cleavage, and demonstrates uneven or conchoidal fracture. Specimens of chrysocolla are typically of massive or earthy habit. The substance may also display reniform or bulbous, botryoidal habit. It lacks macroscopic crystals.

Azurite, malachite and chrysocolla are commonly found in the oxidized zones of copper veins and deposits. Rhodocrosite occurs in veins and hydrothermal replacement deposits in the company of manganese minerals as well as other metal ores such as copper. Photos Native copper has been utilized by humans as a natural resource since perhaps 3,400 B.C. The word 'copper' is derived from the Latin cuprum, which was in turn a modification of the Greek name Kyprios. The word Kyprios indicated the island of Cyprus, where the metal was mined in ancient times. Copper is a member of the class of native elements. The minerals of this class either contain only the atoms of a single element or else are metal alloys. A metal alloy may contain two or more metallic elements in solid solution, but its constituent atoms must be bonded only by metallic bonds. Native copper is a metal and its lattice structure contains only elemental copper. Native copper gains its structure and many of its properties from metallic bonds. When metal atoms bond together into a crystal the valence electrons become delocalized and are free to roam throughout the lattice. The attraction of the positively charged atoms for the surrounding electrons bonds the atoms into an ordered structure.

The positive ions surrounded by the negatively charged electron resevoir retain an almost perfectly spherical shape. In a pure metal, these atoms are all of one element and are therefore all of the same atomic radius. Because the atoms are spherical, equally sized, equally charged, and surrounded by negative, delocalized electrons they pack closely together to form a dense and very ordered crystalline structure. Metals tend to be dense and to have a high degree of symmetry. Copper possesses a typically high density of 8.9 g/cm3 . Parallel planes of equally sized and charged atoms may glide across one another, resulting in the softness, malleability, ductility, and sectility which are characteristic of metals and are demonstrated by native copper. As expected, copper is soft, possessing a hardness of 2 1/2 to 3 on the Mohs scale. The many delocalized valence electrons present within a metallic lattice serve as conducting electrons and account for the high conductivity of metals. Copper, like all native metals, conducts well. Electromagnetic waves cannot propagate through a metal. Instead, they are absorbed and reflected. The absorption index of a metal is very high, and nearly all incident light is reflected.

This renders the metal completely opaque and makes it appear shiny and brilliant. Copper is therefore opaque and will not transmit light in thin section; the mineral possesses a typical shiny, reflective metallic luster. In color, native copper consistently demonstrates the familiar and distinctive copper red; its streak is also red in hue. The red of native copper is an example of idiochromatic coloration, or color which is derived directly from the presence of one of the main constituent elements of the mineral. Idiochromatic color is a property which is directly related to the chemical composition of a mineral species and is therefore possessed by all specimens of that species. This characteristic red of native copper is attributable to the presence of copper, which has strong pigmenting capabilities and is the only constituent of the crystal lattice. (For an introduction to idiochromatism please refer to Section 2 .) Exposed surfaces of native copper crystals may tarnish to black oxide or green carbonate according to the following reaction: 2Cu + O -----------> 2CuCO 3 Native copper has no cleavage and does not tend to break along regular planes. Its fracture is 'hackly', or jagged, containing many small irregularities.

The lattice structure occupied by copper is that of cubic closest packing or face-centered cubic. This type of structure is based around a cube on which an atom occupies each of the eight corners. Atoms are emplaced at the center of each of the six exterior faces as well. This is the most dense of all possible lattice structures. (Please refer to the discussion of crystalline lattices in Section 3 .) Native copper is of the isometric crystal system. Isometric crystals possess four three-fold axes of symmetry and are measured against three axes of equal length which occur at right angles to one another. (Please refer to the discussion of crystal system in Section 3 .) Individual copper crystals may may be of cubic, dodecahedral, tetrahedral, and very rarely of octahedral shape. Aggregates of crystals may be wiry in habit or form a dendritic, arborescent branching structure. (Please refer to the discussion of crystal habit in Section 2 .) Fine mineral specimens with whole individual crystals and well-formed crystal faces are quite rare.

The mineral azurite ( Cu3(CO3)2(OH)2 ) is an ore of copper, and provided human civilization with one of its earliest sources of this metal. Both azurite and its close relative malachite have been mined for thousands of years. Because of its amazing blue color, azurite has long been used as a pigment in dyes and as a decorative gemstone. The species was named 'azurite' in honor of this distinctive azure blue. The mineral is also called 'chessylite', a name reminiscent of Chessy, France, where large quantities have been mined. Single crystals of azurite are a dark, royal blue; the mineral exhibits a brilliant azure blue color when it is of dull or earthy luster. Its streak is blue. This coloration is idiochromatic and is due to the presence of the chromophore copper, which grants a strong pigmenting effect, within the crystal lattice. (Please refer to Section 2 for a discussion of idiochromatism and the chromophores.) Azurite's characteristic blue color is useful in identification.

Azurite produces some specimens of adamantine luster which are very sparkly and highly translucent with a high refractive index. It forms other samples of vitreous or glassy lustre and medium refractive index; its surface may also be rough, giving a dull, earthy and almost lustreless appearance. Azurite possesses a density of 3.77 to 3.83 g/cm 3 and a Mohs scale hardness of 3 1/2 to 4. Its cleavage is good in two directions; its fracture is conchoidal, or shell-like, resulting in a series of concentric rings about the stressed point. The mineral is of brittle tenacity and is not malleable. Like other minerals of the carbonate class, azurite effervesces slightly in hydrochloric acid. This provides a useful means of identification in the field. In shape azurite crystals may be equidimensional; prismatic, or elongated in one dimension; or tabular, appearing in flat plates. Aggregates of crystals are frequently botryoidal in habit, having a globular form said to resemble a bunch of grapes. Azurite may also form radiating crusts or earthy masses.

(Please refer to the description of crystal habit in Section 2 .) Photos The mineral malachite is a semi-precious stone and a common ore of copper. Its name is derived from the greek term malache, 'mallow', which refers to its leaf green color. Like azurite, malachite has been used for centuries as a pigment in dyes and as a semi-precious stone. Malachite may vary from bright to dark green in color; its streak is consistently light green. The coloration of malachite is idiochromatic and due to the presence of copper within the chemical formula ( Cu2Co3(OH)2 ). Specimens may be of adamantine, silky, or dull lustre. Malachite possesses a density between 3.6 and 4.0 g/cm 3 and a hardness of 3 1/2 to 4 on the Mohs scale. It demonstrates perfect cleavage in one direction; however, this cleavage occurs rarely. More frequently observed is the conchoidal or splintery fracture. Large individual crystals of malachite are very rare, but may occur in prismatic form.

Aggregates of crystals are frequently mammillary, forming smooth, bulbous masses. They may also be botryoidal and globular. They may occur in radial assemblages, forming layers and concentric rings in varying colors of green. Malachite is likewise observed to produce fibrous threads and tufts, stalactitic formations, and earthy, incrusted masses. Distinctive concretionary banding patterns occur in many samples, particularly in botryoidal masses. These are caused by varying oxidation levels in the aqueous solution from which dissolved minerals exsolute. The mechanism by which this occurs is not fully understood. (For a discussion of terms such as 'mammillary', 'botryoidal' and 'concretionary' please refer to the description of crystal habit contained in Section 2 .) Classification and Association of Azurite and Malachite Both azurite and malachite are hydroxide-containing members of the copper carbonate class. Carbonate minerals compose a class in which ( CO3 ) 2- anions are linked by various cations within the unit cell. Copper carbonates in particular are hydrous carbonate minerals which contain both the copper cation ( Cu2+ ).

Azurite possesses the chemical formula Cu3(CO3)2(OH)2 ; the formula of malachite is Cu2(CO3)(OH)2 . Azurite and malachite are commonly found together and in conjunction with native copper and other copper ores. Crystal System and Molecular Structure Both azurite and malachite belong to the monoclinic crystal system. Members of this crystal system possess three axes of unequal length, two of which are perpendicular to each other. The end faces are inclined relative to the side faces rather than being orthogonal to them. Such crystals are usually short, having the appearance of a distorted rectangle. (Please refer to the discussion of crystal structure found in Section 3 .) The molecular structure of azurite consists of square groups composed of two ( O2- while azurite possesses a ratio of 1:2 for the same substances. Since Cu(OH)2 is more highly oxidized than CuCO3 and malachite possesses the higher ratio of this cation, malachite thus occupies a later stage in the oxidation process than does azurite. The more prevalent oxidation of malachite is responsible for its bright green color as compared to the deep blue of azurite.

Pseudomorphism in Azurite and Malachite Malachite is more stable than azurite; over time azurite will invert to malachite. Sometimes the external form of the original azurite is preserved during this process. Malachite can thus form a pseudomorph of azurite as azurite unit cells are replaced over time by those of malachite. When a pseudomorph of a crystal forms, the unit cells of the original mineral are gradually replaced cell for cell by those of a new mineral. The original macroscopic crystal shape remains intact, but the chemical substance of which it is composed is now that of a different mineral. Although the external, macroscopic form has been preserved, the internal microscopic structure has changed. A pseudomorph thus possesses the chemical composition of the new mineral species while its external crystal form preserves the shape of the original, replaced species. A pseudomorph of malachite after azurite retains the same shape as the original azurite crystal but is composed of malachite rather than azurite. The pseudomorph is therefore malachite green in color rather than azurite blue.

The chemical formula describing the inversion of azurite to malachite is: 2 Rhodocrosite ( MnCO3 ) is member of the carbonate class and an ore of manganese. Its name is derived from the Greek words rhodon, meaning 'rose', and chros, color. The name was given in reference to the mineral's characteristic rose pink or red color. Rhodocrosite's distinctive pink color is an example of idiochromatism which is due to the presence of the chromophore manganese ( Mn ) in the chemical formula. (Please refer to Section 2 for a discussion of idiochromatism and the chromophores.) This characteristic pink color may darken upon exposure to the atmosphere. Rhodocrosite is known to alter to black manganese oxides or hydroxides. The mineral displays a white streak. It is translucent and will transmit light diffusely; it possesses a vitreous or pearly luster. Rhodocrosite has a density of 3.4 to 3.6 g/cm 3 and a hardness of 3 1/2 to 4 on the Mohs scale. It is brittle and displays uneven fracture.

Like the hydrous copper carbonates azurite and malachite, rhodocrosite is a member of the carbonate class. The carbonate minerals are compounds of a metal or semimetal with the carbonate anion ( CO3)2- . Rhodocrosite is not, however, a hydrous carbonate because it contains neither water ( H2O ) nor the hydroxyl anion ( OH- ). Instead it is a member of calcite group. The minerals of the calcite group possess a simple geometry in which layers of ( CO3)2- radicals alternate with layers of ( 2+ ) metallic cations. Ionic bonds join the carbonate anions to the metallic cations. Rhodocrosite and all calcite group minerals are of rhombohedral crystal system. Crystals of this system are measured against three vertical axes which intersect one another at 120° angles and one horizontal axis which is perpendicular to the other three. A rhombohedron may be envisioned as an equilateral parallelogram which has been turned up onto one corner. (For more information on crystal systems, please refer to Section 3 .) The cleavage of rhodocrosite is perfect in three directions.

Like the cleavage of all minerals of the calcite group, it is rhombohedral. Crystals are rare but may be rhombohedral; more typically the mineral demonstrates botryoidal, encrusting habit. Rhodocrosite is found in veins and hydrothermal replacement deposits in the company of manganese minerals as well as other metal ores. It may alter to manganese oxides or hydroxides. The hydrous silicate chrysocolla ( Cu2H2Si2O5(OH)4 ) is an ore of copper. The name of the species is derived from the Greek words chrysos, meaning gold, and kolla, 'glue'. It was given this name because it strongly resembled a similar material which was once used to solder gold. Chrysocolla is a hydrous or basic copper silicate because it contains the hydroxyl anion ( OH- ). Unlike true minerals it does not possess a crystalline lattice. Instead it is an amorphous 'silica gel' or gelatinous precipitate. Because it is amorphous and lacks a crystalline structure, chrysocolla is not a mineral in the strictest sense.

However, it is a copper-bearing solid substance which is found in the oxidized zones of copper veins and is associated with minerals such as azurite, malachite, cuprite, and native copper. In color chrysocolla is green to sky-blue. This coloration is idiochromatic and is due to the presence of the chromophore copper ( Cu ) within the material. The streak is very pale blue or green. Chrysocolla is translucent and is able to transmit light when sliced into thin sheets. Samples may be of vitreous or glassy luster; they may also appear greasy, dull, or earthy. Chrysocolla is quite soft, possessing a hardness of 2 - 4 on Mohs scale; it has a density of 2.0 - 2.4 g/cm 3 . It is very brittle, sometimes fragile. It has no cleavage and demonstrates the uneven or conchoidal fracture which is typical of glassy, amorphous materials. This type of fracture displays a series of rounded, concentric rings radiating away from the point of impact. Conchoidal fracture may sometimes be observed on a piece of thick broken glass such as the base of a glass bottle.

Specimens of chrysocolla are typically of massive or earthy habit. The substance may also display reniform or bulbous, lumpy botryoidal habit. It lacks macroscopic crystals. An amusing field test may aid in the identification of chrysocolla. When touched to the tongue a specimen of this substance will usually adhere lightly. It sometimes tastes bitter or basic. Malachite Gemstone Malachite Gemstone Nugget of polished malachite. Photo Credit: Calibas, Wikipedia Commons Sign Up for Our Free Newsletters Thanks, You're in! Health Tip of the Day Recipe of the Day There was an error. Please try again. Please select a newsletter. Please enter a valid email address. Did you mean ? Chemistry Facts and Pictures - Photos and Tables Updated December 30, 2016. Malachite is a copper carbonate with the chemical formula Cu2CO3(OH)2. This green mineral can form monoclinic crystals, but usually is found in massive form. Photo Credit: Calibas, Wikipedia Commons

Question: Malachite is an ore of which chemical element?
Answer: Copper