A Metal is any of a class of substances characterized by high electrical and thermal conductivity as well as by malleability, ductility, and high reflectivity of light. Approximately three-quarters of all known chemical elements are metals. The vast majority of metals are found in ores. Metals are usually crystalline solids. Metals have a relatively simple crystal structure distinguished by a close packing of atoms and a high degree of symmetry. Precious metals are metals that are rare and have a high economic value, due to various factors, including their scarcity, use in industrial processes, and role throughout history as a store of value. The single most popular precious metal for investment purposes is gold, followed by silver. Investors purchase precious metals mainly as a financial asset. The most popular precious metals with investors are gold, platinum, and silver. Here are the 10 most precious metals in the world.

1. Rhodium

Rhodium is a rare, silvery-white, hard, corrosion-resistant chemical element . Rhodium is a member of the platinum group. Rhodium is one of the of the six platinum group metals: platinum, palladium, rhodium, osmium, iridium and ruthenium. It is chemically inert transition metal. It is one of the most valuable precious metals. It was discovered in 1803 by William Hyde Wollaston. Rhodium has both a higher melting point and lower density than platinum. Rhodium is one of the rarest elements in the Earth’s crust. It is mostly mined from Russia, South Africa and Canada. Rhodium it is unaffected by air and water up to 1,112 degrees Fahrenheit (600 degrees Celsius), according to Lenntech. It does not react to oxygen easily. It occurs up to one part per 200 million in the Earth’s crust, according to Chemistry Libretexts.

The primary use of this element is in automobiles as a catalytic converter, changing harmful unburned hydrocarbons, carbon monoxide, and nitrogen oxide exhaust emissions into less noxious gases. Pure rhodium is inert and harmless in elemental form. Rhodium detectors are used in nuclear reactors to measure the neutron flux level and used to form drug precursors and the processes for the production of acetic acid. It is used as an alloying agent for hardening and improving the corrosion resistance of platinum and palladium. It is used for its reflective surfaces in search lights, mirrors and jewellery finish, giving everything it touches a lovely shine. It is also used in electric connections and is alloyed with platinum for aircraft turbine engines.

2. Platinum

Platinum is one of the rare elements in Earth’s crust. Platinum is a dense, malleable, ductile, element. This is highly unreactive, silverish-white transition metal. It is highly precious metal commodity and it is one of the least reactive metals. It occurs mostly in South Africa, which accounts for 80% of the world production. It occurs naturally in the alluvial sands of various rivers, it was first used by pre-Columbian South American natives to produce artifacts. Mostly used for a lot of weapons, aeronautics and dentist equipment due to its high level of resistance.

Platinum is used in catalytic converters, laboratory equipment, electrical contacts and electrodes, platinum resistance thermometers, dentistry equipment, and jewelry. Compounds containing platinum, such as cisplatin, oxaliplatin and carboplatin, are applied in chemotherapy against certain types of cancer. Platinum is often found chemically uncombined as native platinum and as alloy with the other platinum-group metals and iron mostly. It has various applications in photography, zinc etchings, indelible ink, plating, mirrors, porcelain coloring. This highly malleable metal is incredibly resistant to corrosion and sought after for its metallic shine and lustrous look.

3. Gold

Gold is one of the least reactive chemical elements and it occurs naturally. Gold is available in free elemental form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. Gold is a chemical element with dense, soft, malleable, and ductile metal. It is a good conductor of heat and electricity. It was one of the first metals to attract human attention. Because of its unique qualities, gold has been the one material that is universally accepted in exchange for goods and services. Most mined gold is stored as bullion. The term ‘carat’ indicates the amount of gold present in an alloy. 24-carat is pure gold, but it is very soft. 18- and 9-carat gold alloys are commonly used because they are more durable. It is a bright, slightly reddish yellow in color. This color is determined by the frequency of plasma oscillations among the metal’s valence electrons. The world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry. It has emotional, cultural and financial value and different people across the globe buy gold for different reasons.

Gold is a precious metal that has been used for coinage, jewelry, and other arts. Gold’s resistance to corrosion and also used in infrared shielding, colored-glass production, gold leafing, and tooth restoration. Certain gold salts are still used as anti-inflammatories in medicine. It is usually found in nature in a comparatively pure form. Gold is used in art, for decoration and as architectural ornament. This is used in gears for watches, artificial limb joints. It is ideal for protecting electrical copper components because it conducts electricity well. A gold compound is used to treat some cases of arthritis. The metal remains a highly regarded reserve asset, and approximately 45 percent of all the world’s gold is held by governments and central banks for this purpose. About 1500 tonnes of gold are mined each year. About two-thirds of this comes from South Africa and most of the rest from Russia. A total of 197,576 tonnes of gold exists above ground, as of 2019.

4. Ruthenium

Natural ruthenium consists of a mixture of seven stable isotopes. It is a hard, white transition metal. Russian-born scientist of Baltic-German ancestry Karl Ernst Claus discovered this element in 1844 at Kazan State University. Ruthenium is generally found in ores with the other platinum group metals in the Ural Mountains and in North and South America. Silver-grey ruthenium metal looks like platinum but is rarer, harder, and more brittle. Ruthenium is a chemical element and is inert to most other chemicals. The composition of the mined platinum group metal (PGM) mixtures varies widely, depending on the geochemical formation. For example, the PGMs mined in South Africa contain on average 11% ruthenium while the PGMs mined in the former USSR contain only 2%. Ruthenium, like the other platinum group metals, is obtained commercially as a by-product from nickel, and copper, and platinum metals ore processing. Because of its high melting point, ruthenium is not easily cast; its brittleness, even at white heat, makes it very difficult to roll or draw into wires.

It is used in some jewellery as an alloy with platinum. Most ruthenium produced is used in wear-resistant electrical contacts and thick-film resistors. During electro refining of copper and nickel, noble metals such as silver, gold, and the platinum group metals precipitate as anode mud, the feedstock for the extraction. Most is used in the electronics industry for chip resistors and electrical contacts. Ruthenium oxide is used in the chemical industry to coat the anodes of electrochemical cells for chlorine production. Ruthenium is also used in catalysts for ammonia and acetic acid production. Ruthenium compounds can be used in solar cells, which turn light energy into electrical energy. The industrial application of metallic ruthenium is restricted to use as an alloy for platinum and other metals of the platinum group. Roughly 30 tonnes of ruthenium are mined each year.

5. Iridium

Iridium also has the highest density of all the elements. Iridium is not affected by acids, bases, or most other strong chemicals. Iridium is the most corrosion-resistant element even at temperatures as high as 2000 °C (on the Periodic Table of Elements). It is very rare and is used in platinum alloys. A precious, silver-white metal, iridium is hard and brittle, but it becomes ductile and can be worked at a white heat, from 1,200°. Iridium is found in meteorites in much higher abundance than in the Earth’s crust. It is one of the densest terrestrial substances. Iridium is considered to be the second-densest metal. Iridium’s modulus of elasticity is the second-highest among the metals. Iridium was discovered in 1803 among insoluble impurities in natural platinum. Smithson Tennant, the primary discoverer, named iridium.

Iridium is one of the rarest elements in Earth’s crust, with annual production and consumption of only three metric tons. The most important iridium compounds in use are the salts and acids it forms with chlorine, though iridium also forms a number of organo metallic compounds used in industrial catalysis, and in research. A member of the platinum group metals, iridium is white, resembling platinum, but with a slight yellowish cast. Because of its hardness, brittleness, and very high melting point, solid iridium is difficult to machine, form, or work. It is the only metal to maintain good mechanical properties in air at temperatures above 1,600 °C (2,910 °F). It used for pen tips and compass bearings. It was used in making the standard metre bar, which is an alloy of 90% platinum and 10% iridium. It is also used for the contacts in spark plugs because of its high melting point and low reactivity.

6. Osmium

A gray-white metal, osmium is very hard, brittle, and difficult to work, even at high temperatures. It is the densest naturally occurring element. Pure osmium metal does not occur in nature. British chemist Smithson Tennant discovered osmium in 1803 in the residue left when crude platinum was dissolved by aqua regia. It is a bluish-white transition metal in the platinum group that is found as a trace element in alloys, mostly in platinum ores. The element’s abundance in the Earth’s crust is among the rarest, with an abundance of only 50 ppt in the earth’s crust. It is approximately twice as dense as lead and slightly denser than iridium. It has a very low compressibility. Of the platinum metals it has the highest melting point, so fusing and casting are difficult. Osmium has seven naturally occurring isotopes, six of which are stable.

Osmium powder reacts slowly with the oxygen of the air and gives off detacteble amounts of osmium tetroxide vapour. Osmium is mainly found alloyed with other platinum metals, from which it is recovered commercially. The most important ores are either iridosmine and osmiridium. Iridosmine is a rare mineral found in Russia and in North and South America. It is used to produce very hard alloys for fountain pen tips, instrument pivots, needles and electrical contacts. It is also used in the chemical industry as a catalyst. Osmium wires were used for filaments of early incandescent lamps before the introduction of tungsten. Osmium tetroxide, OsO4, is highly toxic concentrations in air as low as 10-7 g m-3 can cause lung congestion, skin damage, and severe eye damage.

7. Palladium

Palladium is unique in its ability to absorb hydrogen and very malleable element. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. Palladium, platinum, rhodium, ruthenium, iridium and osmium form a group of elements referred to as the platinum group metals (PGMs). They have similar chemical properties. Palladium has the lowest melting point and is the least dense of them. Palladium is a key component of fuel cells, which react hydrogen with oxygen to produce electricity, heat, and water. Russia was the top producer with 82,000 kilograms, followed by South Africa, Canada and the U.S. Russia’s company Norilsk Nickel ranks first among the largest palladium producers globally, accounting for 39% of the world’s production. More than half the supply of palladium and its congener platinum is used in catalytic converters, which convert as much as 90% of the harmful gases in automobile exhaust into less noxious substances.

Palladium is also used in electronics, dentistry, medicine, hydrogen purification, chemical applications, groundwater treatment, and jewelry. Palladium is used in small amounts (about 0.5%) in some alloys of dental amalgam to decrease corrosion and increase the metallic lustre of the final restoration. Palladium heated to 800 °C will produce a layer of palladium(II) oxide (PdO). Palladium is also used watch making, blood sugar test strips, aircraft spark plugs, surgical instruments, and electrical contacts. Palladium is also used to make professional transverse flutes. Palladium can be used for component and connector plating in consumer electronics and in soldering materials. Unlike platinum, palladium may discolor at temperatures above 400 °C (752 °F) due to oxidation, making it more brittle and thus less suitable for use in jewelry.

8. Rhenium

Rhenium is a silvery-white metal with one of the highest melting points of all elements, exceeded by only tungsten and carbon. It also has one of the highest boiling points of all elements, and the highest among stable elements. Rhenium is extremely hard and a heavy metal. Rhenium is one of the rarest elements in the Earth’s crust. Rhenium has the third-highest melting point and second-highest boiling point of any stable element at 5903 K. Rhenium is expensive, with price reaching an all-time high. Rhenium has a hexagonal close-packed crystal structure. Rhenium does not occur free in nature or as a compound in any distinct mineral; instead it is widely distributed in small amounts in other minerals, usually in concentrations averaging about 0.001 parts per million. It resists wear and corrosion very well. Rhenium was discovered in 1908 and it is the second-last stable element to be discovered. The isolation of rhenium was finally achieved in May 1925 by Walter Noddack and Ida Tacke working in Berlin.

Rhenium was the second last-discovered of the elements that have a stable isotope. It is used in the combustion chambers, turbine blades, and exhaust nozzles of jet engines. These alloys contain up to 6% rhenium, making jet engine construction the largest single use for the element. The second-most important use is as a catalyst: rhenium is an excellent catalyst for hydrogenation and isomerization, and is used for example in catalytic reforming of naphtha for use in gasoline. These alloys are used for oven filaments and x-ray machines. It is also used as an electrical contact material as it resists wear and withstands arc corrosion. Rhenium catalysts are used for the hydrogenation of fine chemicals. Some rhenium is used in nickel alloys to make single-crystal turbine blades. It is used on filaments, electronic casings and often comes as by-product of copper mining.

9. Silver

Silver is a relatively soft, shiny metal. It tarnishes slowly in air as sulfur compounds react with the surface forming black silver sulfide. Silver is a white, lustrous transition metal. It exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. Silver has long been valued as a precious metal. The metal is found in the Earth’s crust in the pure, free elemental form, as an alloy with gold and other metals, and in minerals such as argentite and chlorargyrite. Most silver is produced as a byproduct of copper, gold, lead, and zinc refining. It is probable that both gold and silver were used as money by 800 BCE in all countries between the Indus and the Nile. This metal constitutes 0.05 part per million of Earth’s crust. Silver is found generally in lead ores, copper ores, and cobalt arsenide ores and is also frequently associated with gold in nature. Silver also contain the important metals lead, copper, or zinc or a combination of the three. Alloys of silver with copper are harder, tougher, and more fusible than pure silver and are used for jewelry and coinage.

Silver has antibacterial properties and silver nanoparticles are used in clothing to prevent bacteria from digesting sweat and forming unpleasant odours. Silver is used in solar panels, water filtration, jewellery, ornaments, high-value tableware and utensils, in electrical contacts and conductors, in specialized mirrors, window coatings, in catalysis of chemical reactions, as a colorant in stained glass and in specialised confectionery. Its compounds are used in photographic and X-ray film. Silver also finds use as a catalyst for its unique ability to convert ethylene to ethylene oxide, which is a precursor of many organic compounds. Silver is used to make mirrors, as it is the best reflector of visible light known. It is also used in dental alloys, solder and brazing alloys, and batteries. Silver paints are used for making printed circuits. Silver threads are woven into the fingertips of gloves so that they can be used with touch screen phones.

10. Indium

Indium is a soft, ductile, malleable, lustrous metallic metal with silvery white color which is used in the semiconductor industry, in low-melting- point metal alloys such as Lead-free solders. It is stable in air and water. Indium is named after the bright indigo line in its spectrum. Our Indium products include indium ingot, indium granules, indium foil, indium wire, indium coin, Indium Ribbon, indium oxide etc. It is not an alkali metal. It is a post-transition metal that makes up 0.21 parts per million of the Earth’s crust. Indium was discovered in 1863 by Ferdinand Reich and Hieronymous Theodor Richter by spectroscopic methods. Indium is a minor component in zinc sulfide ores and is produced as a byproduct of zinc refinement. Indium is considered a technology-critical element. The density of indium, 7.31 g/cm3, is also greater than gallium, but lower than thallium. Indium Foil is made by pure Indium Ingot which is very soft and shapable metal. Indium foil has great thermal conductivity.

Indium is produced exclusively as a by-product during the processing of the ores of other metals. Its main source material are sulfidic zinc ores. Minor amounts are probably also extracted from sulfidic copper ores. The primary consumption of indium worldwide is LCD production. Popularity of LCD computer monitors and television sets, which now account for 50% of indium consumption. The first large-scale application for indium was coating bearings in high-performance aircraft engines to protect against damage and corrosion. Now it can be found in fusible alloys, solders, and electronics. Indium(III) oxide and indium tin oxide (ITO) are used as a transparent conductive coating on glass substrates in electroluminescent panels. Indium nitride, phosphide and antimonide are semiconductors used in transistors and microchips. An indium alloy has been used for fire-sprinkler systems in shops and warehouses because of its low melting point. People can be exposed to indium in the workplace by inhalation, ingestion, skin contact, and eye contact leads to lung disease.

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