| In chemistry, the term base metal is | | | | each have an ISO 4217 currency code. |
| used informally to refer to a metal that | | | | The best-known precious metals are gold |
| oxidizes or corrodes relatively easily, | | | | and silver. While both have industrial |
| and react variably with dilute | | | | uses, they are better known for their |
| hydrochloric acid (HCl) to form | | | | uses in art, jewelry, and coinage. Other |
| hydrogen. Examples include iron, nickel, | | | | precious metals include the Platinum |
| lead and zinc. Copper is considered a | | | | group metals: ruthenium, rhodium, |
| base metal as it oxidizes relatively | | | | palladium, osmium, iridium, and |
| easily, although it does not react with | | | | platinum, of which platinum is the most |
| HCl. It is commonly used in opposition | | | | widely traded. |
| to noble metal. | | | | The demand for precious metals is driven |
| In alchemy, a base metal was a common | | | | not only by their practical use, but |
| and inexpensive metal, as opposed to | | | | also by their role as investments and a |
| precious metals, mainly gold and silver. | | | | store of value. Palladium is, as of |
| A longtime goal of the alchemists was | | | | February 20 2007, valued at ($337.50 USD |
| the transmutation of base metals into | | | | per ounce) slightly above half the price |
| precious metals. | | | | of gold ($658.58 USD/ounce), and |
| In numismatics, coins used to derive | | | | platinum ($1210.50 USD/ounce) at around |
| their value primarily from the precious | | | | twice that of gold. Silver is |
| metal content. Most modern currencies | | | | substantially less expensive ($13.84 USD |
| are fiat currency, allowing the coins to | | | | ounce) than these metals, presently at |
| be made of base metal. | | | | about 1/50 the price of gold, but is |
| One method of classifying metals is by | | | | often traditionally considered a |
| their content, and one common division | | | | precious metal for its role in coinage |
| is into ferrous metals and non-ferrous | | | | and jewellery. Rhodium though is the |
| metals. The term ferrous is derived from | | | | most expensive of the precious metals |
| the Latin "Ferrum" which means | | | | with prices as high as $6200.00 USD per |
| "containing iron", thus ferrous metals | | | | ounce (as of December 29, 2006). |
| contain iron and non ferrous metals do | | | | Bullion |
| not. Ferrous metals may be pure iron, | | | | Precious metals in bulk form are known |
| like wrought iron, or they may be alloys | | | | as bullion, and are traded on commodity |
| of iron and other elements. Steel, being | | | | markets. Bullion metals may be cast into |
| an alloy of iron and carbon, would | | | | ingots, or minted into coins. The |
| therefore be a ferrous metal. | | | | defining attribute of bullion is that it |
| Ferrous metals are often magnetic, but | | | | is valued by its mass and purity rather |
| this property is not in and of itself | | | | than by a face value as money. Many |
| sufficient to classify a metal as | | | | nations mint bullion coins, of which the |
| ferrous or non-ferrous. Austenitic | | | | most famous is probably the gold South |
| stainless steel, a ferrous metal, is | | | | African Krugerrand. Although nominally |
| non-magnetic, while cobalt is magnetic | | | | issued as legal tender, these coins' |
| but non-ferrous. However since ferrous | | | | face value as currency is far below that |
| metals are the most common magnetic | | | | of their value as bullion. For instance, |
| materials, magnets are commonly used to | | | | the United States mints a gold bullion |
| separate them from non-ferrous metals | | | | coin (the Gold Eagle) at a face value of |
| and other materials. | | | | $50 containing 1 troy ounce (31.1035 g) |
| Common ferrous metals include the | | | | of gold — as of January 2006, this |
| various irons and steels. Common | | | | coin is worth about $550 as bullion. |
| non-ferrous metals include aluminium, | | | | Bullion coins' minting by national |
| tin, copper, zinc, and brass, an alloy | | | | governments gives them some numismatic |
| of copper and zinc. The precious metals | | | | value in addition to their bullion |
| silver, gold, and platinum are also | | | | value, as well as certifying their |
| non-ferrous. | | | | purity. The level of purity varies from |
| Noble metals are metals that are | | | | country to country, with some bullion |
| resistant to corrosion or oxidation, | | | | coins of as pure as 99.99% available, |
| unlike most base metals. They tend to be | | | | such as the Canadian Gold Maple Leaf. |
| precious metals, often due to perceived | | | | Note that a 100% pure bullion is not |
| rarity. Examples include gold, silver, | | | | possible, as absolute purity in |
| tantalum, platinum, and rhodium. | | | | extracted and refined metals can only be |
| Some of the noble metals can be | | | | asymptotically approached. |
| dissolved in aqua regia, a highly | | | | One of the largest bullion coins in the |
| concentrated mixture of acids. | | | | world is the 10,000 dollar Australian |
| Alchemists were concerned with the | | | | Gold Nugget coin minted in Australia |
| transmutation of base metals into gold | | | | which consists of a full kilogram of |
| (a noble metal) for economic gain, or as | | | | 99.9% pure gold; however China has |
| a metaphor for more esoteric processes. | | | | produced coins in very limited |
| The term can also be used in a relative | | | | quantities (less than 20 pieces minted) |
| sense. A "Galvanic series" is a | | | | that exceed 260 troy ounces (8 kg) of |
| hierarchy of metals (or other | | | | gold. |
| electrically conductive materials, | | | | Gold as an investment and silver as an |
| including composites and semimetals) | | | | investment are often seen as a hedge |
| that runs from noble to active, and | | | | against both inflation and economic |
| allows designers to see at a glance how | | | | downturn. Silver coins have become |
| materials will interact in the | | | | popular with collectors due to their |
| environment used to generate the series. | | | | relative affordability, and unlike most |
| In this sense of the word, graphite is | | | | gold and platinum issues which are |
| more noble than silver (even though it | | | | valued based upon the markets, silver |
| is alchemically more base) and the | | | | issues are more often valued as |
| relative nobility of many materials is | | | | collectables, far higher than their |
| highly dependent upon context, as for | | | | actual bullion value. |
| aluminium and stainless steel in | | | | Precious metal status |
| conditions of varying pH. | | | | A metal is deemed to be precious if it |
| In physics the definition of a noble | | | | is rare. The discovery of new sources of |
| metal is even more strict. It is | | | | ore or improvements in mining or |
| required that the d-bands of the | | | | refining processes may cause the value |
| electronic structure are filled. Taking | | | | of a precious metal to diminish. The |
| this into account, only copper, silver | | | | status of a "precious" metal can also be |
| and gold are noble metals, as all d-like | | | | determined by high demand or market |
| band are filled and don't cross the | | | | value. |
| Fermi level. For platinum two d-bands | | | | An interesting case of a once-precious |
| cross the Fermi level, changing its | | | | metal that is now common is that of |
| chemical behaviour; it is used (in | | | | aluminium. Although aluminium is one of |
| contrast to e.g. gold) as a catalyst. | | | | the most commonly occurring elements on |
| The different reactivity can easily be | | | | Earth, it was initially found to be |
| seen while preparing clean metal | | | | exceedingly difficult to extract from |
| surfaces in ultra high vacuum; surfaces | | | | its various ores. This made aluminium |
| of noble metals (e.g. gold) are easy to | | | | more valuable than gold. Bars of |
| clean and stay clean for a long time, | | | | aluminium were exhibited alongside the |
| while those of e.g. platinum or | | | | French crown jewels at the Exposition |
| palladium are covered by carbon monoxide | | | | Universelle of 1855, and Napoleon III |
| very quickly. | | | | was said to have reserved a set of |
| Precious metals in bulk form are known | | | | aluminium dinner plates for his most |
| as bullion. A precious metal is a rare | | | | honored guests. Additionally, the |
| metallic chemical element of high | | | | pyramidal top to the Washington Monument |
| economic value. | | | | is made of pure aluminium, as at the |
| Chemically, the precious metals are less | | | | time of the monument's construction, |
| reactive than most elements, have high | | | | aluminium was more expensive than |
| luster, and have higher melting points | | | | silver, gold, or platinum. Over time, |
| than other metals. Historically, | | | | however, the price of the metal |
| precious metals were important as | | | | gradually dropped; the discovery of the |
| currency, but are now regarded mainly as | | | | Hall-Héroult process in 1886 caused the |
| investment and industrial commodities. | | | | high price of aluminium to permanently |
| Gold, silver, platinum and palladium | | | | collapse. |