Gold is a soft, dense, yellow metal that barely reacts with anything, which is why a gold ring found in the ground can look almost as bright as the day it was lost. Humans have treasured it for thousands of years, yet it is also a hard-working element that sits inside your phone, your teeth and even the mirrors of a space telescope.
Gold (Au) is a chemical element with atomic number 79: a dense, unreactive transition metal that is yellow, very malleable and found in nature as the pure metal. This guide covers the properties of gold, where it comes from, how to spot the real thing, and what it is used for.
What is gold?
Gold is a chemical element with the symbol Au and atomic number 79, so every gold atom has 79 protons in its nucleus. Its relative atomic mass is 196.97. It sits in group 11 of the periodic table, in period 6, directly below silver and copper. It is a transition metal, and it is also called a noble metal because it resists corrosion and oxidation so well.
The English word “gold” comes from an old root meaning “yellow” or “bright”. The symbol Au comes from the Latin aurum, often linked to the idea of “shining dawn”. Both names point to the same thing: colour. Along with copper, gold is one of the very few metals that is not silvery-grey, and it keeps that colour because it does not tarnish.
That combination explains why people prized it. Gold is rare, it is found as a shiny metal rather than locked in an ore, it is soft enough to shape with simple tools, and it never rusts. The sections below explain exactly which physical and chemical properties make that possible.
Where does gold come from?
Every atom of gold on Earth was made in space, long before the Sun existed. Stars like our Sun cannot make it. Gold needs a violent environment with an enormous supply of free neutrons, where atomic nuclei capture neutrons faster than they can decay. This is called the rapid neutron-capture process, or r-process.
The best-understood source is the collision of two neutron stars, the dense remnants of exploded stars. In 2017, astronomers detected gravitational waves and light from one such merger, an event called GW170817. The glow it produced, known as a kilonova, showed signs of freshly made heavy elements, including gold. Some rare types of supernova may also contribute.
That gas and dust cloud collapsed to form the Sun and planets, and the gold came along with it. You can read more about the formation of the solar system. Lighter elements are far more abundant, and you can compare gold with the most common element in the universe to see how rare it really is.
Most of the gold that was in the young Earth did not stay near the surface. While the planet was molten, dense iron sank to the centre to form the core, and it took most of the gold with it. Much of the gold in the crust today is thought to have arrived later, delivered by meteorites bombarding the planet. Scientists still debate the details.
Where is gold found on Earth?
Gold is very scarce in the crust: about 0.004 parts per million, or roughly 4 mg in every tonne of rock. Mined ore typically contains only a few grams of gold per tonne, so miners must process tonnes of rock to get enough for a single ring.
Because gold is so unreactive, it is usually found as native gold, meaning the uncombined metal. It occurs as nuggets, flakes and tiny grains of metal that can be seen with the naked eye, rather than being chemically locked inside a compound like iron or aluminium.
There are two main types of deposit:
- Lode deposits: gold in veins of quartz and other hard rock, formed when hot, mineral-rich water deposited it in cracks deep underground.
- Placer deposits: gold grains and nuggets that weathering has freed from the rock and rivers have carried away. Being so dense, the gold settles in river gravels, which is why panning works.
Natural gold nearly always contains some silver. A natural gold–silver alloy with more than 20 % silver is called electrum. Gold also forms a few compounds in nature, mainly telluride minerals such as calaverite (AuTe₂) and sylvanite. Some gold is also recovered as a by-product of refining other metals: when copper is purified by electrolysis, gold collects in the anode sludge. To learn how these materials are classified, see our guide to rocks and minerals.
Fool’s gold vs real gold: how to tell them apart
Many people have been fooled by a glittering yellow rock. Fool’s gold is pyrite, iron(II) disulfide (FeS₂). It is a completely different mineral, and a few simple tests separate it from real gold.
| Property | Gold | Pyrite (fool’s gold) |
|---|---|---|
| Colour | Deep, rich yellow | Brassy, pale yellow |
| Streak (colour of powder on unglazed porcelain) | Golden-yellow | Greenish-black |
| Hardness (Mohs) | 2.5–3 (soft) | 6–6.5 (hard) |
| Density | 19.3 g/cm³ | About 5 g/cm³ |
| Malleability | Malleable: dents and flattens | Brittle: shatters or crumbles |
| Crystal shape | Rarely well-formed; nuggets, flakes, grains | Often sharp cubes |
| Reaction to a knife | Scratched easily; can be cut or dented | Not scratched by a steel knife; sparks and may smell of sulfur when struck with steel |
Physical properties of gold
The physical properties of gold explain why people have treasured it for thousands of years. It is dense, soft, shiny and easy to shape, and it keeps its glow without polishing. Like other metals on the periodic table, it conducts electricity and heat, but it has a few extreme features all of its own.
| Physical property | Value | Why it matters |
|---|---|---|
| Melting point | 1,064 °C | Can be melted and cast with a furnace or torch |
| Boiling point | 2,856 °C | Very stable at high temperatures |
| Density | 19.3 g/cm³ | Feels surprisingly heavy; hard to fake |
| Hardness (Mohs) | 2.5–3 | Soft, so pure gold scratches and dents |
| Electrical conductivity | Third best metal, after silver and copper | Reliable electrical contacts that never corrode |
| Infrared reflectivity | Over 98 % | Used on space telescopes and visors |
| Magnetism | Diamagnetic | Not attracted to a magnet |
These values also fit the general patterns in the periodic table: gold is a dense transition metal in group 11 with a high melting point.
Malleability and ductility
Gold is the most malleable and ductile of all metals. A single gram can be beaten into a sheet of about 1 m², and gold leaf can be around 0.1 µm thick. That is so thin that it lets greenish light pass through.
The same gram can also be drawn into a wire more than 2 km long. This is possible because the layers of gold atoms slide over one another easily without the metal breaking.
Density
With a density of 19.3 g/cm³, gold is about 19.3 times heavier than the same volume of water. A one-litre carton filled with gold would have a mass of roughly 19.3 kg, which is more than most people could comfortably carry far. This high density comes from the heavy atoms (79 protons each) packed closely together, and it is one of the easiest ways to separate real gold from imitations.
Electrical and thermal conductivity
Gold is the third best electrical conductor among the metals, behind silver and copper. It is also an excellent conductor of heat. Silver and copper are better at carrying current, but they tarnish. Gold stays clean, so it is chosen for tiny contacts where a reliable connection matters more than cost.
Softness
Pure gold measures just 2.5–3 on the Mohs scale. A fingernail is about 2.5, so you can nearly scratch pure gold with it. This is why jewellers mix gold with other metals to make it hard-wearing, as explained in the section on purity later in this article.
Is gold magnetic?
No. Gold is diamagnetic, which means it is very weakly repelled by a magnetic field. You will not notice this with an ordinary magnet.
Why is gold yellow?
Most metals look silvery because they reflect all colours of visible light about equally. Gold absorbs some blue light and reflects yellow and red, so it looks golden.
Beyond GCSE: the reason is relativity. Gold’s nucleus has 79 protons, so the inner electrons move at a large fraction of the speed of light. This makes the 6s orbital contract and shrinks the energy gap between the 5d and 6s electrons, so blue light has just the right energy to be absorbed.
The same effect holds the outer electron tightly. Gold’s first ionisation energy is 890 kJ/mol, which helps explain why it is so unreactive.
Chemical properties of gold
The chemical properties of gold can be summed up in one word: unreactive. Gold is a “noble metal”. Its electron configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s¹, and it holds on to its electrons so firmly that few substances can persuade it to react.
Why gold does not rust or tarnish
Gold does not react with air, water or oxygen, even when heated. Rusting is a reaction between iron, oxygen and water, and gold simply does not take part. It also resists single common acids.
In the reactivity series of metals, gold sits at or near the bottom, usually drawn as … copper, silver, gold, platinum. A metal this low down does not displace anything and does not corrode, which is why ancient gold objects look as bright as the day they were made.
What dissolves gold? Aqua regia
Gold does dissolve in aqua regia (“royal water”), a mixture of 3 parts concentrated hydrochloric acid to 1 part concentrated nitric acid by volume. Neither acid can do it alone, but together they can.
Nitric acid oxidises gold to Au³⁺ ions. The chloride ions from hydrochloric acid then lock these up as [AuCl₄]⁻, removing them from the solution so that more gold keeps dissolving.
Au + HNO₃ + 4HCl → HAuCl₄ + NO + 2H₂O
Gold and cyanide
Gold also dissolves in a solution of sodium or potassium cyanide when oxygen is present. This reaction is the basis of modern gold mining, where it is used to pull tiny specks of gold out of crushed rock.
4Au + 8NaCN + O₂ + 2H₂O → 4Na[Au(CN)₂] + 4NaOH
Cyanide is highly poisonous, so the process must be tightly controlled.
Gold and mercury
Mercury dissolves gold to form an amalgam, a mixture of mercury with another metal. Small-scale miners have long used this to collect gold from river sediment, then heated the amalgam to boil the mercury away.
The mercury vapour is a serious health and pollution problem. The Minamata Convention, agreed in 2013, aims to cut its use.
Gold compounds and oxidation states
Although gold rarely reacts, it can form compounds. The two common oxidation states are +1 (gold(I), also called aurous) and +3 (gold(III), also called auric). Gold(III) chloride is a well-known example. These compounds are easily broken down again, which is why gold readily returns to its metallic form.
Because gold is so unreactive, it is found in nature as native gold, uncombined with other elements. Most metals lose electrons much more easily and are found only in compounds.
How is gold mined and extracted?
Gold is rare, so getting it out of the ground takes a lot of rock and a lot of chemistry. Because gold is unreactive and often found as native metal, extraction is simpler in principle than for most metals, but the tiny concentrations make it hard work in practice. In outline, the journey from rock to a gold bar follows these steps.
- Exploration: geologists survey, sample and drill to find ore that is worth mining.
- Mining: the ore is dug out of the ground by open-pit, underground or placer methods.
- Crushing and grinding: the rock is broken into fine powder so the gold is exposed.
- Concentrating: gravity separation and/or froth flotation collect the gold-rich material.
- Cyanide leaching: the gold is dissolved, then captured on carbon (carbon-in-pulp).
- Electrowinning and smelting: the gold is recovered and cast into doré bars of gold and silver.
- Refining: doré is purified to 99.5 % or 99.99 % gold.
Mining methods
The method depends on how the gold lies in the ground. Open-pit mining removes rock from a huge stepped hole and suits ore close to the surface. Underground mining follows deep quartz veins through shafts and tunnels.
Placer (alluvial) mining targets gold grains and nuggets that rivers have washed into gravel. Because gold is so dense, water carries lighter sand away and leaves the gold behind. This is the oldest method, and it is still used today.
Separating gold from rock
Mined ore typically holds only a few grams of gold per tonne, so most of the work is separation. After crushing and grinding, gravity separation takes advantage of gold’s density of 19.3 g/cm³. Panning, sluices and shaking tables all let water wash away light rock while heavy gold settles out.
Froth flotation is used when gold is locked inside other minerals. The ground ore is mixed with water and chemicals, and air is blown through it. Gold-bearing particles stick to the bubbles and are skimmed off as a froth.
Fine gold is then dissolved by cyanide leaching, using the cyanide reaction shown above. Gold dissolves as a soluble complex, and carbon-in-pulp adsorption pulls it out of the solution onto activated carbon. The gold is then recovered by electrowinning and smelted into doré bars.
Refining gold to 99.99 %
Doré is only part-way to pure gold, because it still contains silver and other metals. Refineries use two main processes.
In the Miller process, chlorine gas is bubbled through molten doré. Silver and other metals form chlorides that float off as a slag, leaving gold of about 99.5 % purity.
The Wohlwill process goes further. Impure gold is the anode in a gold chloride solution, and pure gold plates onto the cathode. This is an application of electrolysis, and it gives gold that is 99.99 % pure.
The environmental cost of gold mining
Gold mining can do serious harm if it is poorly managed. Cyanide is highly toxic, and spills such as the one at Baia Mare in Romania in 2000 poisoned rivers. Small-scale miners often use mercury to form an amalgam with gold. Mercury then pollutes air, water and food chains, which is why the Minamata Convention was agreed in 2013.
There is also the waste. Mining can generate tonnes of rock for a single ring, along with large amounts of energy use and land disturbance.
Recycling helps. Old jewellery, electronics and dental gold can be melted and refined again, and recycling supplies roughly a quarter of the gold that reaches the market each year. You can read more about why recycling metal matters.
How much gold is there?
According to the World Gold Council, about 216,000 tonnes of gold had been mined by the end of 2024. That would fit into a cube roughly 22 m on each side. Mines produce about 3,600 tonnes a year, and recent leading producers include China, Russia, Australia, Canada and the USA.
Gold purity: carats, fineness and coloured gold
Pure gold is soft, so most gold items are alloys. Purity is measured in carats (spelled karats in the USA), which are parts of gold out of 24. So 18 carat gold is 18 parts gold and 6 parts other metals, or 75 %. Do not confuse this with the carat used for diamonds, which measures mass.
A second system, fineness, gives parts of gold per thousand. It is the number stamped on the item.
| Carat | Gold content | Fineness mark | Typical use |
|---|---|---|---|
| 24 ct | 99.9 % | 999 | Bullion bars, coins, investment |
| 22 ct | 91.7 % | 916 | Wedding rings, traditional jewellery |
| 18 ct | 75.0 % | 750 | Fine jewellery, watches |
| 14 ct | 58.5 % | 585 | Everyday jewellery (mainly USA) |
| 10 ct | 41.7 % | 417 | Budget jewellery (mainly USA) |
| 9 ct | 37.5 % | 375 | Everyday jewellery in the UK |
White, rose and green gold
The colour of gold alloys depends on the metals mixed in. White gold is gold alloyed with palladium, or with nickel and silver, and is often plated with rhodium for a bright finish. Rose (red) gold contains more copper, which gives it a pink-red tint. Green gold contains more silver.
Adding other metals also makes gold harder, which is why alloys are better than pure gold for rings that are worn every day.
Hallmarks in the UK
In the UK, gold articles above 1 g must be hallmarked by an Assay Office before they can be sold. The hallmark includes the fineness, so you can check what you are buying. 9 ct is the lowest purity that can legally be sold as gold in the UK.
Uses of gold
The uses of gold come straight from its properties. It is unreactive, so it never corrodes. It is soft and malleable, so it is easy to shape. It conducts electricity well, reflects infrared radiation, and looks beautiful. Few other elements combine all of these.
Jewellery
Jewellery is the largest single use of gold, accounting for roughly half of demand. Because gold does not tarnish, a ring can look the same after centuries. Pure gold is too soft for everyday wear, so jewellers alloy it with other metals to make it harder.
Money, investment and central banks
Gold bars and coins are bought as a store of value, and central banks hold gold as part of their reserves. Of the gold above ground, roughly 22 % is held as bars, coins and exchange-traded funds, and about 17 % is held by central banks. Gold is scarce, cannot be corroded away, and is accepted worldwide, which is why it has been used as money for thousands of years.
Electronics and technology
Gold is used in connectors, edge contacts on circuit boards and the tiny bonding wires inside computer chips. A copper contact slowly corrodes and can cause faults, but gold stays clean, so the connection stays reliable. A mobile phone contains only a few tens of milligrams of gold, but billions of devices add up to a large amount.
Many of these parts are not solid gold. A very thin layer is applied by gold plating, which uses electricity to deposit the metal. You can read more about the process in our guide to electrolysis and electroplating.
Medicine and dentistry
Dentists have long used gold for crowns because it is inert, malleable and does not corrode in the mouth. In medicine, the gold salts sodium aurothiomalate and auranofin were once used to treat rheumatoid arthritis, although newer drugs have largely replaced them.
You may have used gold nanoparticles without knowing it. They produce the red line in many lateral flow tests, including pregnancy tests and rapid COVID-19 tests. Radioactive gold-198 has also been used in some forms of cancer brachytherapy, where a radioactive source is placed close to a tumour.
Space exploration
Gold reflects infrared radiation extremely well, which makes it ideal for space. The 18 beryllium mirror segments of the James Webb Space Telescope are coated with a thin layer of gold, about 48 g in total, so that they reflect infrared light from distant galaxies. Astronaut helmet visors carry a thin gold film that reflects harmful radiation and glare, and gold-coated foil insulates satellites.
Art, architecture and food
Gold leaf decorates domes, picture frames and illuminated manuscripts. Because it can be beaten so thin and never tarnishes, it keeps its shine for centuries. Edible gold leaf is used to decorate some food and drinks, and gold is approved as the food additive E175. It passes through the body unchanged.
Catalysis
Bulk gold is famously unreactive, but gold nanoparticles can speed up some reactions. In the 1980s, Masatake Haruta showed that tiny gold particles are surprisingly good catalysts for oxidising carbon monoxide. This work opened up a whole area of research into gold catalysts.
A short history of gold
- c. 4,500 BC: The Varna necropolis in Bulgaria contains the oldest known worked gold hoard.
- Ancient Egypt: Gold was linked with the gods and pharaohs. Tutankhamun’s funeral mask contains about 10 kg of gold.
- c. 600 BC: The first coins appear in Lydia, in modern Turkey. They were made of electrum, the natural gold–silver alloy.
- Middle Ages: Alchemists tried for centuries to turn lead into gold. It cannot be done by chemical reactions, because chemistry cannot change one element into another.
- 1848–1855: The California Gold Rush draws hundreds of thousands of prospectors to the western USA.
- 1931 and 1971: The UK leaves the gold standard in 1931, and the USA ends the convertibility of dollars into gold in 1971.
- 1980: Glenn Seaborg’s team makes tiny amounts of gold from bismuth using a particle accelerator. The cost is far greater than the value of the gold.
Gold vs silver vs copper
Copper, silver and gold sit together in group 11 of the periodic table. Their properties show clear trends and some important differences.
| Property | Copper | Silver | Gold |
|---|---|---|---|
| Symbol | Cu | Ag | Au |
| Atomic number | 29 | 47 | 79 |
| Density | 8.96 g/cm³ | 10.5 g/cm³ | 19.3 g/cm³ |
| Melting point | 1,085 °C | 962 °C | 1,064 °C |
| Colour | Reddish | Silvery white | Yellow |
| Electrical conductivity | Second best | Best of all metals | Third best |
| In air | Slowly tarnishes, forming a green patina | Tarnishes black with sulfur compounds | Does not tarnish |
These three metals were used for coins because they share useful features. All are soft enough to stamp, conduct well, and resist corrosion better than most metals. That makes them durable, and silver and gold are rare enough to hold their value. Gold is the most resistant of the three, which is why it was the most prized.
Myths and misconceptions about gold
Key points to remember about gold
Frequently asked questions about gold
What are the main properties of gold?
Gold is a shiny yellow, very dense (19.3 g/cm³) and soft metal. It is the most malleable and ductile of all metals, conducts heat and electricity well, melts at 1,064 °C and is extremely unreactive, so it does not rust, tarnish or react with most acids.
What is gold used for?
The biggest use of gold is jewellery, followed by investment bars and coins and central bank reserves. Smaller but important amounts go into electronics, dentistry, medical tests, space equipment such as telescope mirrors and astronaut visors, decorative gold leaf and chemical catalysts.
Why is gold so unreactive?
Gold holds its outer electron very tightly, so it is hard for gold to lose electrons and form ions. That places it at or near the bottom of the reactivity series. Beyond GCSE, the extra-strong hold comes from relativistic effects caused by its heavy nucleus of 79 protons.
Does gold rust or tarnish?
No. Pure gold does not react with oxygen or water, so it never rusts or tarnishes. Low-carat gold jewellery can darken slightly over time, but that is caused by the other metals in the alloy, such as copper or silver, not by the gold itself.
Is gold magnetic?
No. Gold is diamagnetic, which means it is not attracted to a magnet (it is actually very weakly repelled). If a piece of “gold” jewellery sticks to a magnet, it contains other metals such as iron or nickel.
What can dissolve gold?
Gold dissolves in aqua regia, a mixture of three parts concentrated hydrochloric acid and one part concentrated nitric acid. It also dissolves in cyanide solution when oxygen is present, which is how most gold is extracted from ore, and it forms an amalgam with mercury.
Where does gold come from?
Gold was made in space, mainly in collisions between neutron stars, through the rapid neutron-capture (r-) process. It was already present in the cloud of gas and dust that formed the solar system. On Earth it is mined from quartz veins and river gravels.
How can you tell real gold from fool’s gold?
Fool’s gold is pyrite (FeS₂). Real gold is deeper yellow, soft enough to dent, leaves a golden-yellow streak and is almost four times as dense. Pyrite is pale and brassy, brittle, too hard to scratch with a knife and leaves a greenish-black streak.
What is the difference between 24 carat, 22 carat and 18 carat gold?
Carat measures purity in parts out of 24. 24 carat gold is 99.9 % pure, 22 carat is 91.7 % gold and 18 carat is 75 % gold. Lower carats are harder and cheaper because more of the alloy is made of other metals such as copper, silver or palladium.
Why is gold so expensive?
Gold is rare (about 4 mg in a tonne of crustal rock), costly to mine and refine, and it never corrodes, so it keeps its value for centuries. Steady demand from jewellery, investors and central banks, plus its uses in technology, keeps the price high.
