Precious Metal

Precious metals occupy a special place in chemistry, the economy and cultural history. The term derives not from an arbitrary convention but from a clear electrochemical criterion: a metal is considered noble if its standard electrode potential relative to the normal hydrogen electrode is positive — that is, thermodynamically stable against oxidation in aqueous solution. This explains why gold coins still gleam metallically after thousands of years, while iron objects crumble into rust.

Which metals belong to the group?

In chemistry, eight elements are usually counted as precious metals: gold, silver, platinum and palladium, along with the four rarer platinum group metals rhodium, iridium, ruthenium and osmium. In commercial usage the term often narrows to the first four, as only these are widely traded on international futures markets.

Sources: IUPAC standard values; potentials against the normal hydrogen electrode (NHE).

The basic electrochemical principle

The decisive criterion distinguishing precious metals from base metals such as copper, iron or aluminium is the positive standard potential. The higher this value, the greater the thermodynamic driving force to keep the metal in its elemental form.

Ox + n e⁻  →  Red     E° > 0 V  ⟹  noble
Ox + n e⁻  →  Red     E° < 0 V  ⟹  base

A classic example: gold dissolves neither in concentrated hydrochloric acid nor in concentrated nitric acid. Only the mixture of both acids — so-called aqua regia (3 parts HCl : 1 part HNO₃) — attacks gold, by creating a new driving force via chloro complexes.

Physical properties

All precious metals share a range of outstanding material properties:

• Corrosion resistance: no stable oxide layer forms; the surface remains metallically bright.
• High density: all precious metals are heavier than most base metals; osmium is the densest element of all.
• Good electrical conductivity: silver has the highest electrical conductivity of all elements (6.3 × 10⁷ S/m).
• Ductility: gold in particular can be rolled into wafer-thin gold leaf (< 0.1 µm) or drawn into the finest wire.
• Catalytic action: platinum and palladium accelerate chemical reactions without being consumed themselves — the basis of the automotive catalytic converter.

Occurrence and extraction

Precious metals occur in the Earth's crust in very low concentrations. Gold frequently occurs native (as pure metal in rock or river sands), while platinum group metals are mostly obtained as a by-product of nickel and copper mining. To date, an estimated 210,000 tonnes of gold have been mined worldwide — an amount that would form a cube about 22 metres on each edge.

Primary extraction involves open-pit and underground mining; the ore obtained passes through several processing stages up to the doré bar, which is then brought to fineness at a refinery. Alongside this, recycling — particularly from electronic scrap and old jewellery — is becoming increasingly important (urban mining).

Significance as an investment asset

Owing to their scarcity, durability and universal acceptance, physical precious metals have traditionally been regarded as an inflation hedge and a safe haven in times of crisis. The current gold price and silver price reflect the worldwide balance of supply (mine production + recycling) and demand (jewellery, industry, investors, central banks).

The notional material value of physical objects — whether bars, coins or old jewellery — is determined by the melt value calculator. It combines weight, fineness and the current spot price.

Note: Information on tax matters (e.g. VAT exemption for investment gold, Capital Gains Tax) and on value development does not constitute tax or investment advice. For individual questions, consult a qualified accountant or investment adviser.

Distinction: semi-precious metals and related terms

Not every corrosion-resistant metal is a precious metal in the electrochemical sense. Copper (E° = +0.34 V) formally lies above the hydrogen electrode, yet it visibly tarnishes and forms a patina — it is therefore classified as a precious metal or a borderline case depending on context. Titanium and niobium are resistant thanks to a protective passivation layer, but count as base metals because of their negative standard potential. The term semi-precious metal is not sharply defined in chemistry and is used inconsistently in trade.

In brief

Precious metals are those whose positive electrochemical standard potential permanently protects them from corrosion. Gold, silver, platinum and palladium are the economically most significant representatives — as a raw material for industry and jewellery just as much as a physical store of value, whose prices are traded around the clock on global markets.