Precious Metal
Also: Precious metals, Noble metals
Precious metals are a group of chemical elements characterised by high resistance to corrosion and oxidation, and which occur in nature predominantly in native form — that is, in pure metallic form.
Precious metals occupy a special position in chemistry, economics and cultural history. The term does not derive 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 — meaning it is thermodynamically stable against oxidation in aqueous solution. This explains why gold coins still gleam metallically after thousands of years, while iron objects crumble to rust.
Which Metals Are Included?
In chemistry, eight elements are usually counted as precious metals: gold, silver, platinum and palladium, as well as the four rarer platinum group metals rhodium, iridium, ruthenium and osmium. In commercial usage, the term is often narrowed to the first four, as only these are widely traded on international futures markets.
| Metal | Symbol | Atomic number | Density (g/cm³) | Melting point (°C) | Std. potential (V) |
|---|---|---|---|---|---|
| Gold | Au | 79 | 19.32 | 1,064 | +1.50 |
| Silver | Ag | 47 | 10.49 | 962 | +0.80 |
| Platinum | Pt | 78 | 21.45 | 1,768 | +1.19 |
| Palladium | Pd | 46 | 12.02 | 1,555 | +0.95 |
| Rhodium | Rh | 45 | 12.41 | 1,964 | +0.76 |
| Iridium | Ir | 77 | 22.56 | 2,446 | +1.16 |
| Ruthenium | Ru | 44 | 12.37 | 2,334 | +0.45 |
| Osmium | Os | 76 | 22.59 | 3,033 | +0.40 |
Sources: IUPAC standard values; potentials against normal hydrogen electrode (NHE).
Electrochemical Fundamental Principle
The decisive distinguishing criterion 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 maintain the metal in elemental form.
Ox + n e⁻ → Red E° > 0 V ⟹ noble
Ox + n e⁻ → Red E° < 0 V ⟹ base
Classic example: gold dissolves in neither concentrated hydrochloric acid nor concentrated nitric acid. Only the mixture of both acids — the 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 number 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 ultra-thin gold leaf (< 0.1 µm) or drawn into the finest wire.
- Catalytic effect: Platinum and palladium accelerate chemical reactions without being consumed in the process — the basis of the automotive catalytic converter.
Occurrence and Extraction
Precious metals occur in the Earth's crust in very low concentrations. Gold frequently appears in native form (as pure metal in rock or river sands), while platinum group metals are mostly obtained as a by-product of nickel and copper mining. Worldwide, an estimated total of around 210,000 tonnes of gold has been mined to date — a quantity that would form a cube with an edge length of approximately 22 metres.
Primary extraction includes open-pit and underground mining; the extracted ore passes through several processing stages up to the doré bar, which is subsequently refined to fine metal content at a refinery. In addition, recycling — particularly from electronic scrap and old jewellery — is gaining increasing importance (urban mining).
Significance as an Investment
Due to their scarcity, durability and universal acceptance, physical precious metals are traditionally regarded as inflation protection and a safe haven in times of crisis. The current gold price and silver price reflect the global balance between supply (mine production + recycling) and demand (jewellery, industry, investors, central banks).
The calculated material value of physical objects — whether bars, coins or scrap jewellery — is determined by the melt value calculator. It combines weight, fineness and the current spot price.
Note: Information on tax aspects (e.g. VAT exemption for investment gold, speculative holding period under § 23 EStG) and on value performance does not constitute tax or investment advice. For individual questions, please consult a qualified tax advisor or investment advisor.
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, but visibly tarnishes and forms patina — it is therefore classified as either a precious metal or a borderline case depending on context. Titanium and niobium are resistant due to a protective passivation layer, but are classified as base metals because of their negative standard potential. The term semi-precious metal is not precisely defined in chemistry and is used inconsistently in trade.
In Brief
Precious metals are those metals whose positive electrochemical standard potential protects them permanently from corrosion. Gold, silver, platinum and palladium are the economically most significant representatives — as a raw material for industry and jewellery as well as a physical investment whose prices are traded around the clock on global markets.