Metal types

In chemistry, the term base metal is used informallyThe best-known precious metals are gold and silver.
to refer to a metal that oxidizes or corrodesWhile both have industrial uses, they are better
relatively easily, and react variably with diluteknown for their uses in art, jewelry, and coinage.
hydrochloric acid (HCl) to form hydrogen. ExamplesOther precious metals include the Platinum group
include iron, nickel, lead and zinc. Copper is consideredmetals: ruthenium, rhodium, palladium, osmium, iridium,
a base metal as it oxidizes relatively easily, although itand platinum, of which platinum is the most widely
does not react with HCl. It is commonly used intraded.
opposition to noble metal.The demand for precious metals is driven not only by
In alchemy, a base metal was a common andtheir practical use, but also by their role as
inexpensive metal, as opposed to precious metals,investments and a store of value. Palladium is, as of
mainly gold and silver. A longtime goal of theFebruary 20 2007, valued at ($337.50 USD per ounce)
alchemists was the transmutation of base metals intoslightly above half the price of gold ($658.58 USD
precious metals.ounce), and platinum ($1210.50 USD/ounce) at around
In numismatics, coins used to derive their valuetwice that of gold. Silver is substantially less
primarily from the precious metal content. Mostexpensive ($13.84 USD/ounce) than these metals,
modern currencies are fiat currency, allowing thepresently at about 1/50 the price of gold, but is
coins to be made of base metal.often traditionally considered a precious metal for its
One method of classifying metals is by their content,role in coinage and jewellery. Rhodium though is the
and one common division is into ferrous metals andmost expensive of the precious metals with prices as
non-ferrous metals. The term ferrous is derived fromhigh as $6200.00 USD per ounce (as of December
the Latin "Ferrum" which means "containing iron", thus29, 2006).
ferrous metals contain iron and non ferrous metals doBullion
not. Ferrous metals may be pure iron, like wroughtPrecious metals in bulk form are known as bullion, and
iron, or they may be alloys of iron and otherare traded on commodity markets. Bullion metals may
elements. Steel, being an alloy of iron and carbon,be cast into ingots, or minted into coins. The defining
would therefore be a ferrous metal.attribute of bullion is that it is valued by its mass and
Ferrous metals are often magnetic, but this propertypurity rather than by a face value as money. Many
is not in and of itself sufficient to classify a metal asnations mint bullion coins, of which the most famous
ferrous or non-ferrous. Austenitic stainless steel, ais probably the gold South African Krugerrand.
ferrous metal, is non-magnetic, while cobalt isAlthough nominally issued as legal tender, these coins'
magnetic but non-ferrous. However since ferrousface value as currency is far below that of their
metals are the most common magnetic materials,value as bullion. For instance, the United States mints
magnets are commonly used to separate them froma gold bullion coin (the Gold Eagle) at a face value of
non-ferrous metals and other materials.$50 containing 1 troy ounce (31.1035 g) of gold
Common ferrous metals include the various irons and— as of January 2006, this coin is worth
steels. Common non-ferrous metals include aluminium,about $550 as bullion. Bullion coins' minting by national
tin, copper, zinc, and brass, an alloy of copper andgovernments gives them some numismatic value in
zinc. The precious metals silver, gold, and platinum areaddition to their bullion value, as well as certifying
also non-ferrous.their purity. The level of purity varies from country
Noble metals are metals that are resistant toto country, with some bullion coins of as pure as
corrosion or oxidation, unlike most base metals. They99.99% available, such as the Canadian Gold Maple
tend to be precious metals, often due to perceivedLeaf. Note that a 100% pure bullion is not possible, as
rarity. Examples include gold, silver, tantalum, platinum,absolute purity in extracted and refined metals can
and rhodium.only be asymptotically approached.
Some of the noble metals can be dissolved in aquaOne of the largest bullion coins in the world is the
regia, a highly concentrated mixture of acids.10,000 dollar Australian Gold Nugget coin minted in
Alchemists were concerned with the transmutationAustralia which consists of a full kilogram of 99.9%
of base metals into gold (a noble metal) for economicpure gold; however China has produced coins in very
gain, or as a metaphor for more esoteric processes.limited quantities (less than 20 pieces minted) that
The term can also be used in a relative sense. Aexceed 260 troy ounces (8 kg) of gold.
"Galvanic series" is a hierarchy of metals (or otherGold as an investment and silver as an investment
electrically conductive materials, including compositesare often seen as a hedge against both inflation and
and semimetals) that runs from noble to active, andeconomic downturn. Silver coins have become popular
allows designers to see at a glance how materials willwith collectors due to their relative affordability, and
interact in the environment used to generate theunlike most gold and platinum issues which are valued
series. In this sense of the word, graphite is morebased upon the markets, silver issues are more often
noble than silver (even though it is alchemically morevalued as collectables, far higher than their actual
base) and the relative nobility of many materials isbullion value.
highly dependent upon context, as for aluminium andPrecious metal status
stainless steel in conditions of varying pH.A metal is deemed to be precious if it is rare. The
In physics the definition of a noble metal is evendiscovery of new sources of ore or improvements in
more strict. It is required that the d-bands of themining or refining processes may cause the value of
electronic structure are filled. Taking this into account,a precious metal to diminish. The status of a
only copper, silver and gold are noble metals, as all"precious" metal can also be determined by high
d-like band are filled and don't cross the Fermi level.demand or market value.
For platinum two d-bands cross the Fermi level,An interesting case of a once-precious metal that is
changing its chemical behaviour; it is used (in contrastnow common is that of aluminium. Although aluminium
to e.g. gold) as a catalyst. The different reactivity canis one of the most commonly occurring elements on
easily be seen while preparing clean metal surfaces inEarth, it was initially found to be exceedingly difficult
ultra high vacuum; surfaces of noble metals (e.g. gold)to extract from its various ores. This made aluminium
are easy to clean and stay clean for a long time,more valuable than gold. Bars of aluminium were
while those of e.g. platinum or palladium are coveredexhibited alongside the French crown jewels at the
by carbon monoxide very quickly.Exposition Universelle of 1855, and Napoleon III was
Precious metals in bulk form are known as bullion. Asaid to have reserved a set of aluminium dinner
precious metal is a rare metallic chemical element ofplates for his most honored guests. Additionally, the
high economic value.pyramidal top to the Washington Monument is made
Chemically, the precious metals are less reactive thanof pure aluminium, as at the time of the monument's
most elements, have high luster, and have higherconstruction, aluminium was more expensive than
melting points than other metals. Historically, precioussilver, gold, or platinum. Over time, however, the
metals were important as currency, but are nowprice of the metal gradually dropped; the discovery
regarded mainly as investment and industrialof the Hall-Héroult process in 1886 caused the
commodities. Gold, silver, platinum and palladium eachhigh price of aluminium to permanently collapse.
have an ISO 4217 currency code.