A precious metal is defined as a rare chemical element that occurs naturally and has high economic value. Gold, silver, platinum, palladium and rhodium are a few of the most popular precious metals that are used for similar purposes, although there are significant differences in their economic value. These metals are used most frequently as investments, merchandise and for medical and dental equipment. We researched these precious metals to learn the differences between them and what makes their respective market values differ so greatly.
Gold is a dense, soft, shiny, malleable and ductile metal. Gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive chemical elements solid under standard conditions. The metal therefore occurs often in free elemental (native) form, as nuggets or grains in rocks, in veins and in alluvial deposits. Less commonly, it occurs in minerals as gold compounds, usually with tellurium.
Gold resists attacks by individual acids, but it can be dissolved by the aqua regia (nitro-hydrochloric acid), so named because it dissolves gold. Gold also dissolves in alkaline solutions of cyanide, which have been used in mining. Gold dissolves in mercury, forming amalgam alloys. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to confirm the presence of gold in items, giving rise to the term the acid test.
Gold has been a valuable and highly sought-after precious metal for coinage, jewelry, and other arts since long before the beginning of recorded history. Gold standards have been the most common basis formonetary policies throughout human history, being widely supplanted by fiat currency starting in the 1930s. The last gold certificate and gold coin currencies were issued in the U.S. in 1932. In Europe, most countries left the gold standard with the start of World War I in 1914 and, with huge war debts, failed to return to gold as a medium of exchange.
A total of 165,000 tonnes of gold have been mined in human history, as of 2009. This is roughly equivalent to 5.3 billion troy ounces or, in terms of volume, about 8500 m3, or a cube 20.4 m on a side. The world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry.
Besides its widespread monetary and symbolic functions, gold has many practical uses in dentistry,electronics, and other fields. Its high malleability, ductility, resistance to corrosion and most other chemical reactions, and conductivity of electricity led to many uses of gold, including electric wiring, colored-glass production and even gold leaf eating.
It has been claimed that most of the Earth's gold lies at its core, the metal's high density having made it sink there in the planet's youth. Virtually all of the gold that mankind has discovered is considered to have been deposited later by meteorites which contained the element.
Silver is a very ductile, malleable (slightly harder than gold), monovalent coinage metal, with a brilliant white metallic luster that can take a high degree of polish. It has the highest electrical conductivity of all metals, even higher than copper, but its greater cost has prevented it from being widely used in place of copper for electrical purposes. An exception to this is in radio-frequency engineering, particularly at VHF and higher frequencies, where silver plating to improve electrical conductivity of parts, including wires, is widely employed. During World War II 13,540 tons were used in the electromagnets used for enriching uranium, mainly because of the wartime shortage of copper.
Among metals, pure silver has the highest thermal conductivity (the nonmetal carbon in the form of diamond and superfluid helium II are higher) and one of the highest optical reflectivities. (Aluminium slightly outdoes silver in parts of the visible spectrum, and silver is a poor reflector of ultraviolet). Silver also has the lowest contact resistance of any metal. Silver halides are photosensitive and are remarkable for their ability to record a latent image that can later be developed chemically. Silver is stable in pure air and water, but tarnishes when it is exposed to air or water containing ozone or hydrogen sulfide, the latter forming a black layer of silver sulfide which can be cleaned off with dilute hydrochloric acid.
As a pure metal, platinum is silvery-white, lustrous, ductile, and malleable. Platinum is more ductile than gold, silver and copper, thus being the most ductile of pure metals, but gold is still more malleable than platinum. It does not oxidize at any temperature, although it is corroded by halogens, cyanides, sulfur, and caustic alkalis. Platinum is insoluble in hydrochloric and nitric acid, but dissolves in hot aqua regia to form chloroplatinic acid.
Platinum's resistance to wear and tarnish is well suited for making fine jewelry. The metal has an excellent resistance to corrosion and high temperature and has stable electrical properties. All of these characteristics have been used for industrial applications.
Palladium is a soft silver-white metal that resembles platinum. It is the least dense and has the lowest melting point of the platinum group metals. It is soft and ductile when annealed and greatly increases its strength and hardness when it is cold-worked. Palladium dissolves slowly in sulfuric, nitric and hydrochloric acid. This metal also does not react with oxygen at normal temperatures (and thus does not tarnish in air). Palladium heated to 800°C will produce a layer of palladium(II) oxide (PdO). It lightly tarnishes in moist atmosphere containing sulfur.
Rhodium is a hard, silvery, durable metal that has a high reflectance. Rhodium metal does not normally form an oxide, even when heated. Oxygen is absorbed from the atmosphere only at the melting point of rhodium, but is released on solidification. Rhodium has both a higher melting point and lower density than platinum. It is not attacked by most acids: it is completely insoluble in nitric acid and dissolves slightly in aqua regia.