Rarest Metal on Earth: Francium, Rhodium, Astatine

Francium is the rarest metal on Earth by total amount: the Royal Society of Chemistry (RSC) says less than one kilogram of it exists in the whole crust at any moment, because it decays with a 22-minute half-life (RSC, francium). Astatine is scarcer still, but chemists place it among the halogens, not the metals. The rarest metal you could actually hold, one that does not decay, is rhodium, and the RSC calls it the rarest of all non-radioactive metals (RSC, rhodium).

Which one is “right” depends on the question you are really asking. This page sorts the answers by what is counted, shows the crust data and the rhodium price history with dates, then moves on to the rare earth metals, the byproduct metals that few people can name, and a calculator that turns parts per billion into tonnes of rock.

Rarest metal answers by question: one table

Most lists mix four different ideas of “rare”: how much exists in total, how thinly it is spread through rock, whether the element counts as a metal, and whether it occurs in nature or only in a reactor. The table keeps them apart.

How these answers were ranked

Three kinds of source sit behind the page. Element facts (discoverers, half-lives, uses, classification) come from the RSC periodic table. Crust grades come from the RSC data pages and from a compilation of CRC Handbook values, because the two disagree on the platinum-group metals. Prices and production come from the USGS Mineral Commodity Summaries 2026 and, for rhodium and gold today, from Kitco quotes dated 26 October 2026.

Synthetic elements made one atom at a time in accelerators are left out, because they do not occur in the crust at all. Californium-252 is covered separately for the same reason. Where two sources disagree, the text says so instead of picking one silently.

Astatine: the rarest element, but not a metal

Astatine (atomic number 85) was first made in 1940 at the University of California by Dale Corson, Kenneth MacKenzie and Emilio Segrè, who bombarded bismuth with alpha particles (RSC, astatine). It also forms naturally for a short time inside the uranium and thorium decay chains, then disappears again. Its longest-lived isotope has a half-life of only about 8 hours, so the stock never builds up.

How much exists is an estimate, not a measurement. The RSC’s podcast text, quoting a standard inorganic chemistry reference, puts it at under 50 milligrams in the top kilometre of crust. Other published estimates for the whole crust range from under one gram to about 28 grams, which shows how loose the figure is. Either way, it is the smallest natural inventory of any element.

It is not a metal by the usual classification. The RSC lists astatine in Group 17 with iodine and chlorine and says it has no uses outside research. In 2013 Andreas Hermann, Roald Hoffmann and Neil Ashcroft published calculations in Physical Review Letters predicting that condensed astatine would be a monatomic metal and possibly a superconductor (University of Edinburgh record of the paper). Nobody can test that, because a visible lump would heat itself until it vaporised.

Astatine price per kilogram or gram

There is no market price. Astatine is not mined and is not sold by weight, and the RSC notes that only tiny amounts have ever been produced. The isotope used in research, astatine-211, is made in a cyclotron from bismuth and has a half-life of 7.21 hours, so it is shipped as radioactivity, not by the gram. Treat any “price per kg” figure on the web as invented.

Francium: the rarest metal by total amount

Marguerite Perey found francium at the Curie Institute in Paris in 1939, but it took until 1946 before her discovery was accepted (RSC, francium). It is an alkali metal in the same group as sodium and potassium, with a melting point of 21°C on the RSC fact box. In practice no one has seen a visible piece. The RSC states that francium has no uses, given its 22-minute half-life, and that it is made in reactors or by bombarding thorium with protons.

That is why it wins the “metal” title: it is the element with the smallest total amount among those that chemists class as metals. The same logic explains why the people who search for a “rarest metal list” often get a different answer from each website. The list is short at the top (francium, then the PGM and rhenium group below) and the order below that depends on the dataset.

Francium price per kilogram

Again there is no price. Francium is made only in research laboratories, so nothing is sold. The only honest answer to “francium price per kg” is that the product does not exist.

Rhodium: the rarest stable metal on Earth

Rhodium was isolated in 1803 by William Hyde Wollaston from platinum ore (RSC, rhodium). The RSC says about 80% of it goes into catalytic converters, where it reduces nitrogen oxides in exhaust, and that world production is about 30 tonnes a year, recovered as a byproduct of copper and nickel refining and from platinum-group ores. South Africa dominates platinum-group mining: it produced an estimated 120,000 kg of platinum in 2025 out of 170,000 kg worldwide (USGS, 2026), and the Bushveld Complex holds the largest reserves.

Chart

Average crust content of the thinnest metals

Parts per billion by mass

How rare in the crust, and why the ranking is not clean

The RSC data page lists rhodium at 0.000037 parts per million (ppm) of the crust. The same figure appears for ruthenium, iridium, osmium, platinum and palladium on their RSC pages, so the number is a shared placeholder-style value that cannot separate them. Rhenium is listed at 0.000188 ppm. Another compilation, based on the CRC Handbook of Chemistry and Physics, gives rhodium, ruthenium, iridium and tellurium all at about 1 part per billion (ppb), osmium at 1.5, and rhenium lower at 0.7 ppb.

So the fair reading is this: rhodium is the metal that the RSC names, and it sits in a group of six or seven metals at roughly one part per billion in the crust, where estimates overlap. Gold at about 4 ppb and platinum at about 5 ppb are only a few times more common on these figures. Newer measurements of the upper crust, such as a 2012 study of Chinese loess, put rhodium near 0.02 ppb, ruthenium 0.03 ppb, iridium 0.02 ppb and platinum near 0.6 ppb, far below the older CRC-based values, though in that study rhodium is still the lowest of the platinum-group metals. Treat any ppb ranking as approximate. Published crustal estimates vary by method (a loess-based upper-crust study, for example, gives far lower values for rhodium and platinum), so the chart uses the CRC Handbook values throughout.

Rhodium price today and how it compares with gold

On 26 October 2026 at 6:35 a.m. Eastern, Kitco showed rhodium at a bid of US$8,625 and an ask of US$9,625 per troy ounce (Kitco rhodium chart). The US$1,000 gap between bid and ask is itself a sign of a thin market. Gold on Kitco at the same time was a bid of US$4,013.80 (Kitco gold chart). At those bids rhodium costs about 2.1 times as much as gold per ounce, not “many times” as sometimes claimed.

Chart

Rhodium annual average price

US$ per troy ounce

Annual averages show how violent the swings are. The USGS gives US$20,254 per troy ounce for 2021, US$15,585 for 2022, US$6,661 for 2023, US$4,660 for 2024 and an estimated US$5,800 for 2025, a rise of 24% on 2024. It links the 2025 rise to lower production and higher demand from hard disk and chemical catalyst users (USGS, Mineral Commodity Summaries 2026, platinum-group metals).

Californium-252: costly, but not a metal you can buy by the tonne

Californium-252 is often called the most expensive element. It does not occur in nature in usable amounts. The US Department of Energy’s National Isotope Development Center lists it as made by successive neutron captures and beta decays of curium isotopes, with a half-life of 2.645 years, and sells it in micrograms (NIDC, Cf-252 product sheet). The sheet gives no per-gram price, so quoted figures in the millions of dollars per gram come from sellers, not from the producer. For a traded metal, rhodium is the answer.

Rhodium next to its platinum-group neighbours

Rhodium rarely stands alone in the data, because it is one of six platinum-group metals (PGMs) that are mined together. The USGS gives the 2025 estimated average price for each, in US dollars per troy ounce, and the spread is wide.

Supply is concentrated. South Africa mined an estimated 120,000 kg of platinum and 70,000 kg of palladium in 2025, Russia 84,000 kg of palladium, and Canada and Zimbabwe smaller amounts. South Africa also holds 63 million kg of the world’s PGM reserves of more than 76 million kg (USGS, 2026). The USGS notes that output in South Africa fell about 9% in 2025 because of deep-level mining costs and power supply problems, which is one reason a thin metal like rhodium can jump when demand rises.

A consultant checking a PGM project should ask which price deck was used for rhodium and whether it is a spot price or a multi-year average, because the table above shows how far one year can sit from the next.

Why some metals are so thin in the crust

Rhodium, iridium, osmium, platinum and gold are called siderophile, or iron-loving. When the young Earth melted, most of them followed iron toward the core, which left the crust with only a thin share. A little came back later through meteorite impacts, and hot fluids then gathered some of it into the veins and reefs that miners work. The same pattern holds for the other metals in the chart. The video below tells the story for gold, and the platinum-group metals follow a similar path.

▶ A short clay explainer on how gold formed in dying stars and reached the crust through hot water. · 4:16

Promethium and the rare earth metals

People who search for the “rarest rare earth” are usually looking at the lanthanide list that starts at lanthanum and ends at lutetium, plus scandium and yttrium. In that family the scarcest by far is promethium (element 61). It has no stable isotope: the RSC says its longest-lived isotope has a half-life of about 18 years, that it is not found naturally on Earth in any amount that can be collected, and that uranium ores hold less than a microgram per million tonnes from spontaneous fission (RSC, promethium). It was first isolated in 1945 at Oak Ridge. There is no mine and no market price.

Chart

Average oxide price of scarce rare earths, 2025 estimate

US$ per kg of oxide

The other rare earths are not rare in the crust; the name refers to how seldom they occur in concentrations worth mining. The USGS notes that rare earths are relatively abundant in the crust but minable concentrations are less common than for most metals. The chart ranks the oxides by average price, which is the practical measure of how hard each one is to get.

Price ranking of the scarce rare earths

Terbium oxide averaged an estimated US$1,010 per kg in 2025 and lutetium oxide US$888 (USGS, rare earths (heavy), 2026). Scandium oxide at 99.99% purity averaged US$640 per kg (USGS, scandium, 2026). Dysprosium oxide was US$239. The common magnet pair, neodymium-praseodymium oxide, averaged US$69 per kg (USGS, rare earths, 2026). These are annual averages for oxides in bulk lots, not spot quotes, and prices inside China can differ from them.

Why one country controls rare earth supply

Mine output of rare earths was an estimated 390,000 tonnes of rare earth oxide equivalent in 2025, and China produced 270,000 tonnes of it, about 69% (USGS, rare earths, 2026). The United States was second at 51,000 tonnes, mostly from Mountain Pass in California, and Australia third at 29,000. The USGS adds that China widened its export controls in October 2025 to cover more elements, including europium and holmium, and then suspended the October measures for one year in November (the April 2025 controls stayed in force).

Chart

Rare earth mine output by country, 2025

Thousand tonnes of oxide equivalent, selected countries

Output of scandium is far smaller: about 80 tonnes worldwide in 2025, all of it as a byproduct of nickel and titanium streams, with China the leading producer (USGS, scandium, 2026). Readers who track licence areas in other producing regions can compare them in our guide to countries richest in minerals.

Obscure metals you have probably never heard of

“Obscure” is not a technical term, but searchers who type it want metals that matter to industry and that almost nobody mines for themselves. These three are good examples, and each is a byproduct, so output depends on a bigger operation. Crust values are from the RSC data pages.

Details on each are in the USGS chapters for gallium, tellurium and rhenium. None is a primary target for a drilling programme. Explorers find them by looking at the base-metal and nickel systems that carry them; for a view of how that works for graphite and battery metals, see graphite exploration and nickel, cobalt and vanadium targets, and for platinum-group supply read South Africa as a platinum and gold supplier.

Calculator: how much rock for one ounce of a rare metal

A figure like “one part per billion” is hard to picture. The calculator below converts a crust grade into tonnes of average rock and a pool count, assuming 100% recovery as the starting case. Real ore is far richer than the crust average, so this shows the scale of the problem, not a mining plan.

Finding scarce metals without drilling first

Metals at one part per billion are never targeted on their own. Explorers look for the host system: a layered intrusion for platinum-group metals, a porphyry for rhenium, a clay deposit for heavy rare earths. Satellite analysis can screen a licence area for the rock types and alteration that go with those systems, and the result is an exploration target that sits ahead of any resource estimate. Rare earth elements are among the materials the Farmonaut platform works with.

If you hold ground and want a screen before spending on drilling, satellite-based mineral detection is one route, and you can send your area through the mining query form or the contact page.

▶ What AI does and does not do in mineral exploration, and how to check a claim. · 4:37

Frequently asked questions

What is the rarest metal on Earth?

Francium, if you count total amount and accept metals only. The RSC says less than a kilogram exists in the crust at any time. Among metals that do not decay, it is rhodium.

What is the rarest element on Earth?

Astatine. The RSC podcast text gives under 50 mg in the top kilometre of crust. It is classed as a halogen, so it does not take the metal title.

Is astatine a metal?

Not by the usual classification. A 2013 calculation by Hermann, Hoffmann and Ashcroft predicted that condensed astatine would be metallic, but no one has been able to make enough to test it.

What is the rarest stable metal on Earth?

Rhodium, per the RSC. Ruthenium, iridium, osmium and rhenium sit close to it in crust tables, so the order inside that group depends on which compilation you use.

What is the rarest rare earth metal?

Promethium. It has no stable isotope and occurs only as a trace from uranium fission. Among the rare earths that are actually traded, terbium and lutetium carry the highest oxide prices in the USGS data.

What is the most expensive element in the world?

For an open market, rhodium, at a Kitco bid of US$8,625 per troy ounce on 26 October 2026. Californium-252 is made only in reactors and is sold by the microgram, so it has no comparable market price.

What is the rarest metal in the universe?

The question has no settled answer. The figures on this page are for Earth’s crust. Astatine and francium are short-lived wherever they occur, so no place in the universe holds a lasting stock of them.

How much does astatine or francium cost per gram?

Neither is sold. They are made in tiny amounts for research and decay within hours or minutes, so a per-gram price has no meaning.

What counts as an obscure metal?

Industrial metals that few people can name: gallium, tellurium and rhenium are common examples. Each is recovered as a byproduct of a larger operation.

Which country mines the most rare earths?

China, with an estimated 270,000 tonnes of oxide equivalent in 2025, about 69% of the world total (USGS, 2026).

Can you find rare metals with satellite images?

Satellites do not see single elements at parts-per-billion levels. They help screen ground for the geology and alteration that host the deposits, which narrows where to sample.