Finding the rarest material in the universe requires defining what “rare” means, as the answer changes dramatically based on the criteria. While materials like iron and silicon are abundant across the cosmos, true rarity often involves conditions of extreme physics or instability. The scarcity of a material can be measured by its low natural abundance in a given environment, such as the Earth’s crust, or by its inherent instability, meaning it decays almost instantly after formation. This conceptual difference distinguishes between elements that are merely hard to find and exotic matter that is fundamentally fleeting.
Defining Rarity: Scarcity vs. Instability
The concept of rarity in matter can be interpreted in two distinct ways: scarcity of atoms or ephemerality of existence. Scarcity refers to the sheer lack of a material’s atoms relative to others, even if the material is stable. For example, a stable element that is a trace component of the Earth’s crust falls into this category, existing permanently but in extremely low concentrations.
Instability relates to materials that decay so quickly that they only exist for a fraction of a second. These materials might be produced constantly through natural processes, but their fleeting half-lives prevent any measurable accumulation. A material can also be considered rare if the conditions required for its existence are found only in the most extreme astrophysical environments. Both definitions present compelling candidates for the title of the universe’s rarest material.
The Rarest Naturally Occurring Elements on Earth
Focusing on the terrestrial environment, the rarest naturally occurring elements are those constantly being produced and destroyed by radioactive decay chains. Astatine (element 85) is considered the rarest element found naturally in the Earth’s crust. It is a decay product of heavier elements, existing only in trace amounts because all of its isotopes are highly radioactive.
The most stable isotope of Astatine, Astatine-210, has a half-life of only 8.1 hours, meaning any sample quickly decays away. Estimates suggest that the entire Earth’s crust contains less than one gram of Astatine at any given time.
Closely following Astatine is Francium (element 87), whose most stable isotope, Francium-223, has a half-life of just 22 minutes. Francium is also a decay product, and its short half-life prevents it from accumulating in weighable quantities. These elements are so scarce and unstable that their properties are largely inferred from their position on the periodic table rather than from direct observation.
Matter Existing Only in Extreme Astrophysical Environments
Rarity on a cosmic scale involves states of matter that require forces and energies not found under normal planetary conditions. One such state is the material found in the core of a neutron star, sometimes referred to as neutron-degenerate matter. This matter is created when a massive star collapses, and gravity crushes electrons into protons through inverse beta decay, resulting in a core composed almost entirely of neutrons.
The density of this matter can exceed 10^17 kilograms per cubic meter, comparable to the density of an atomic nucleus. A single teaspoon of this material would weigh billions of tons on Earth. This extreme density is maintained by neutron degeneracy pressure, a quantum mechanical effect. While neutron stars are numerous, the unique conditions necessary to sustain this matter make it inaccessible.
An even more exotic and ephemeral state is the Quark-Gluon Plasma (QGP), which existed for only milliseconds after the Big Bang. QGP is a state where the fundamental components of protons and neutrons—quarks and gluons—are deconfined and move freely. Under normal conditions, these particles are perpetually bound together.
This deconfined state requires temperatures of approximately 10^12 Kelvin. Scientists can recreate QGP fleetingly by colliding heavy ions, such as gold or lead nuclei, in powerful particle accelerators. The resulting fireball exists for only a fraction of a second before cooling and reverting back into ordinary matter.
Synthetically Created and Ephemeral Elements
The rarest materials are often those that do not exist in nature at all and must be manufactured by human effort. These are the transuranic elements, which have atomic numbers greater than 92 (Uranium) and are synthesized in laboratories. Elements like Tennessine (element 117) and Oganesson (element 118) are examples of ultimate rarity, as only a handful of atoms have ever been successfully created.
Oganesson-294, the only confirmed isotope of element 118, has a half-life of less than one millisecond. Its production involves bombarding a target of Californium-249 with a beam of Calcium-48 ions in a particle accelerator. The process is inefficient, requiring thousands of hours of bombardment to create just a few atoms. The fleeting existence of these atoms makes them the rarest materials that humans have ever directly encountered.