地球上最稀有的金属：铑、钫与稀土元素为何并不稀有

The phrase "rarest metal on earth" sends people looking for a single name, but the answer depends on what you count. This guide sorts out the confusion. It covers which metal is the rarest among the stable ones, which radioactive metal barely exists at all, and why the element often called the rarest of all is a halogen. It also explains why rare earth elements carry a misleading name, how their crustal abundance compares with familiar industrial metals, and where the world's rare earth supply actually comes from.

Table of Contents

• What is the rarest metal on earth?
• Rare in the crust versus rare because it decays
• The rarest stable metals: the platinum group, rhenium and gold
• Why rare earth elements are not rare
• Promethium, the one rare earth that is scarce, and where supply comes from
• Frequently asked questions

The answer depends on whether radioactive metals count. Among stable metals, the Royal Society of Chemistry describes rhodium (opens in a new tab) as the rarest of all non-radioactive metals. If radioactive metals count, francium wins: it is an intensely radioactive alkali metal, and estimates put less than a kilogram of it in the entire crust at any one time. People searching for the rarest element on earth often land on astatine instead. That one is a halogen in group 17, and the top kilometer of the earth's crust is estimated to hold less than 50 mg of it. So the rarest metal on earth has two answers depending on your definition, and the rarest element is a separate question.

The rarest stable metal

Rhodium holds the title among metals that do not decay. It occurs with other platinum metals in river sands in North and South America, and in copper-nickel sulfide ores in Ontario, Canada. Commercial rhodium comes out as a by-product of copper and nickel refining.

Its major use is in catalytic converters for cars, where it reduces nitrogen oxides in exhaust gases.

The rarest metal of all

Francium is scarcer still, and it has no uses. It is made by neutron bombardment of radium or by bombarding thorium with protons. Its half-life is only 22 minutes.

Why astatine is often named instead

Astatine is often described as the rarest naturally occurring element, which pulls it into these searches. Estimates put less than 50 mg of it in the top kilometer of the earth's crust. It is a halogen, and it has no uses outside research. For the rarest metal specifically, the answer is rhodium or francium.

Rare in the crust versus rare because it decays

Two very different situations hide behind the word rare. Some metals are stable and simply present at tiny concentrations, recovered as by-products when other metals are refined. Others are radioactive with short half-lives, so very little exists at any given moment. Both get called rare, but the reasons do not match. Keeping these two apart clears up most of the confusion around the rarest metals.

Stable metals that are simply scarce

The platinum group metals, rhenium and gold fall into this group. They do not decay. Their scarcity shows up as very low concentration spread through rock. Rhodium, iridium, ruthenium and rhenium are recovered commercially as by-products of refining or smelting other metals.

Radioactive metals that barely exist

Francium shows the other kind of rarity. Its atoms break down quickly, so the total amount present at any moment is minute. Promethium behaves this way too among the rare earths, which the later section covers.

A USGS figure lists the nine rarest metals in the crust as the six platinum group elements plus gold, rhenium and tellurium, which USGS labels a metalloid. These are the stable scarce metals. The gap between rare metals and rare earth elements starts here: these metals are scarce in the crust, while most rare earths are not. The Royal Society of Chemistry puts world rhodium production at about 30 metric tons a year and iridium production at about 3 metric tons a year.

Rhodium, iridium and ruthenium

Three of the platinum group metals show how by-product recovery works. Iridium is recovered commercially as a by-product of nickel refining, and the Royal Society of Chemistry notes it is the most corrosion-resistant material known (opens in a new tab). Ruthenium comes from the wastes of nickel refining and is mostly used in electronics for chip resistors and electrical contacts.

Rhodium, covered earlier, is also recovered as a by-product of copper and nickel refining.

Rhenium

Rhenium is among the rarest metals on Earth, spread through the crust at about 0.001 parts per million. It is produced commercially from the flue dusts of molybdenum smelters, and some is added to nickel alloys for single-crystal turbine blades. For high-strength alloys, see the guide to the strongest metal on earth.

Where gold fits

Gold makes the USGS list of the rarest metals in the crust. Royal Society of Chemistry supply data lists its crustal abundance at 0.0013 parts per million. Gold is one of the few elements to occur in a natural state.

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Why rare earth elements are not rare

The USGS view is plain: the persistence of the term rare earth reflects unfamiliarity rather than true rarity. The more abundant rare earths sit at crustal concentrations similar to commonplace industrial metals. Even the two least abundant ones easily outnumber gold. The real scarcity is in concentrated, minable deposits rather than in the ground overall. This is the heart of the difference between rare metals and rare earth elements, and it explains why supply comes from so few places.

The common rare earths match everyday industrial metals

The more abundant rare earths are each similar in crustal concentration to chromium, nickel, copper, zinc, molybdenum, tin, tungsten or lead. Cerium is the most abundant of the lanthanides, more abundant than tin or lead and almost as abundant as zinc. The Royal Society of Chemistry notes cerium (opens in a new tab) is the major component of mischmetal, used in lighter flints, and cerium oxide is used as a catalyst in catalytic converters and self-cleaning ovens.

Even the scarcest rare earths outnumber gold

The USGS states that thulium and lutetium (opens in a new tab), the two least abundant rare earths, are nearly 200 times more common than gold. Thulium is found principally in the mineral monazite and is one of the rarest of the rare earths. Monazite contains about 20 parts per million of it. It is used in portable medical x-ray sources and surgical lasers.

Rare in ore deposits, not in the crust

Rare earths have much less tendency than many common metals to become concentrated in exploitable ore deposits. Most of the world's supply comes from only a handful of sources as a result. The USGS makes the same point in its commodity reporting, noting that rare earths are relatively abundant in the crust while minable concentrations are less common than for most other mineral commodities.

Promethium, the one rare earth that is scarce, and where supply comes from

Promethium is the exception among the rare earths. Its longest-lived isotope has a half-life of only 18 years, so it is not found naturally except in minute amounts in uranium ores. Most of it is used only in research, with a little used in specialized atomic batteries. That makes it the rare earth that actually is rare, for the same decay reason that sidelines francium. The rest of the rare earths depend on mining, and the production and reserve figures tell you where that mining happens.

Promethium

The Royal Society of Chemistry (opens in a new tab) lists most promethium as used only in research. Promethium does not persist in nature beyond the minute amounts found in uranium ores.

Rare earth production and reserves

USGS estimates world rare earth mine production at 390,000 metric tons of rare-earth-oxide equivalent in 2025, with China mining 270,000 metric tons and the United States 51,000 metric tons. In its 2026 summary, USGS puts world reserves at more than 75 million metric tons, with China holding 44 million. Those figures show how concentrated supply is.

Key figures (verified 2026-11-03)

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Frequently asked questions

What is the rarest element on earth?

Astatine is often described as the rarest naturally occurring element. It has been estimated that the top kilometer of the earth's crust contains less than 50 mg of it. Astatine is a halogen in group 17, and it has no uses outside research.

Why are rare earth elements called rare if they are not rare?

The USGS says the name reflects unfamiliarity rather than true rarity. The more abundant rare earths are as common as industrial metals like copper, zinc or lead. Even the two scarcest far outnumber gold. The scarcity is in concentrated, minable deposits, not in the crust overall.

Which rare earth element is actually scarce?

Promethium is the genuine exception. Its longest-lived isotope has a half-life of only 18 years, so it is not found naturally except in minute amounts in uranium ores. Most promethium is used only in research, with a little used in specialized atomic batteries.

Where does the world's rare earth supply come from?

Most of the world's rare earth supply comes from only a handful of sources, because rare earths have much less tendency than many common metals to form exploitable ore deposits. China mines the largest share of world production, and the USGS 2026 summary lists it with 44 million metric tons of reserves. Current production and reserve estimates are in the key figures table on this page.

How is rhodium produced?

Rhodium is obtained commercially as a by-product of copper and nickel refining, and it occurs with other platinum metals in river sands in North and South America and in copper-nickel sulfide ores in Ontario, Canada. Its main use is in catalytic converters for cars, where it reduces nitrogen oxides in exhaust gases.

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