The density (more precisely, the volumetric mass density) of a substance is its mass per unit volume (denoted in kg/m3). It is a unique physical property of an object that shows how tightly matter is packed together that object.
Solid materials like iron and platinum have densely packed particles. In liquids, particles exhibit the ability to slide past one another, while gases consist of particles that freely move in all directions.
In outer space, the densest object known to humanity is the neutron star. These remarkable celestial objects have densities ranging between 3.7×1017 to 5.9×1017 kilogram per meter cube, which is 2.6×1014 to 4.1×1014 times denser than our Sun.
To put this into perspective, one teaspoon of neutron star material would have a mass of about 6.5×1012, which is nearly 1,000 times the mass of the Great Pyramid of Giza.
But what about the Earth? What is the densest material on the Earth, and why are they important? Let’s find out.
Table of Contents
Image Courtesy: John Chapman
Density: 10.28 g/cm3
This might be the first time you have heard about the element named molybdenum. For starters, it belongs to the group of transition metals with an atomic number of 42. It doesn’t occur naturally in a pure metallic form; it only exists in oxidation states in various minerals.
Most molybdenum compounds have high melting points and low solubility in water. They are extensively used in alloys, electrodes, and catalysts.
Molybdenum is commonly used in steel because it increases the strength, hardness, and toughness of the alloy. Almost all ultra-high-strength steels with a yield point of at least 300,000 psi consist of 0.25 to 8% molybdenum.
It is also used as a catalyst to refine petroleum. In the field of biochemistry, it is used as a bacterial catalyst to break atmospheric molecular nitrogen.
And since molybdenum can withstand very high temperatures without softening or expanding, it is also used to manufacture airplane and missile parts, industrial motors, and electrical contacts.
Density: 10.49 g/cm3
Silver is nearly half as dense as gold, which means one gram of silver would be almost double the size of one gram of gold in terms of volume. Although it is not as impressive as gold or platinum, it has many extraordinary properties.
For instance, silver exhibits the highest thermal conductivity, electrical conductivity, and reflectivity compared to any metal. It is found in the Earth’s crust in a free elemental form or in minerals like chlorargyrite and argentite.
From historical times, silver has been valued as one of the crucial minerals on Earth, which is still the case today. Not only has it been used to make currencies, but also ornaments, tableware, and modern electronic products like solar panels.
Since it has high thermal and electrical conductivity, it is extensively used in the electronics industry for developing conductors and coatings.
Density: 11.34 g/cm3
Denser than most commonly used materials, lead has the highest atomic number of any stable substance. It is soft and malleable and has a relatively low melting point. On Earth, lead is one of the commonly found elements alongside sulfur.
Lead’s high atomic weight and tightly packed face-centered cubic structure give it a density of 11.34 grams per centimeter cube, which is higher than common metals like copper, iron, and zinc.
It is now a well-accepted fact that lead was known to humans, even before 6000 BCE, and was probably used for metal smelting. Ancient Egyptians were the first to use lead as a consumer product. Ancient Chinese, on the other hand, used it as a currency.
In the 21st century, lead plays an important role in many industrial sectors (including construction works) due to its high density and extreme tolerance for corrosion.
These properties have been exploited in numerous applications. Lead is used as a barrier to absorb sound, vibration, and radiation. And since it has no natural resonance frequencies, it is used as a sound-deadening layer in the floors, ceilings, and walls of sound studios.
A thin sheet of thorium | Wikimedia
Density: 11.7 g/cm3
Named after Thor, the Norse god of thunder, thorium is a moderately strong radioactive metal whose known isotopes are unstable. This naturally occurring radioactive metal is found in water, rock, and soil.
It is about three times as abundant as uranium in the Earth’s crust. There might be more untapped energy available for use from thorium in the Earth’s crust than from combined uranium and fossil fuel sources. Most of the Earth’s internal heat has been attributed to thorium and uranium.
As per the World Nuclear Association, India has the largest thorium reserve in the world, followed by Brazil, Australia, and the USA.
While thorium is harder than other radioactive materials like plutonium and uranium, it is less dense than both. Its properties vary based on the extent of impurities found in the sample. The most common impurity is thorium dioxide — even the purest samples contain approximately 0.1% of the dioxide.
Today, thorium is used to improve the strength of magnesium, control the grain size of tungsten in electric lamps, coat tungsten wire in electrical instruments, and build heat-resistant ceramics. Moreover, numerous thorium reactors have been constructed to replace uranium in nuclear reactors.
Density: 12.41 g/cm3
Discovered in the early 1800s by English chemist William Wollaston, Rhodium is known for its extreme corrosion resistance and chemically inert characteristics.
It is one of the rarest substances in the Earth’s crust, containing 0.0002 parts per million. This rarity influences its price in the market as well as its use in commercial applications.
Although a large amount of rhodium is retrieved from platinum and other platinum group elements, at least one of its isotopes (103 Rh) is found naturally. Surprisingly, it has also been detected in some potatoes, with concentrations ranging from 0.8 to 30 parts per million.
It has a lower density and a higher melting point compared to platinum. It is not affected by many acids (including nitric acid) but dissolves slightly in aqua regia.
Today, it is mostly used as a catalyst in TWC or three-way catalytic converters (exhaust control systems) in petrol or diesel engines as they help minimize nitric oxide and nitrogen dioxide emissions.
In nuclear reactors, rhodium detectors are used to determine the neutron flux level. It is also alloyed with palladium and platinum to improve hardness and corrosion resistance.
Density: 13.53 g/cm3
Mercury is quite an interesting element in the periodic table. It is one of the two solid elements that become liquid under normal room temperature and pressure, the other being bromine. Its melting and boiling points are −38.8 °C and 356.7 °C.
Its density is about 13.5 times higher than water, so a small amount of mercury feels surprisingly heavy. And since it has a high surface tension, it forms almost spherical beads on glass. When it transforms from liquid to solid, it changes volume by nearly 4% (from 13.69 g/cm3 to 14.184 g/cm3).
Since mercury expands and contracts in a fixed manner with temperatures, it is used in manometers, barometers, thermometers, sphygmomanometers, float valves, and various other devices. However, its use in sphygmomanometers and thermometers has largely been phased out because of its toxic nature.
Today, it is primarily used for electronic applications and manufacturing industrial chemicals. Gaseous mercury, for instance, is used in fluorescent lamps, mercury (II) chloride serves as a catalyst in the production of polyvinyl chloride (PVC), and solid mercury(II) sulfide is used as a pigment in rubber, plastic, and paints.
Density: 16.69 g/cm3
Earlier known as tantalium, it belongs to the refractory group of metals, which constitutes a minor portion of different types of alloys. It’s dense, ductile, and highly conductive to electricity and heat.
Solid tantalum has a body-centered cubic crystal structure with Young’s modulus of 186 GPa and yield stress of 331 MPa. While the metal is very hard, it is known for its corrosion resistance property — even at temperatures lower than 150 °C, tantalum doesn’t react with aggressive aqua regia (a mixture of nitric acid and hydrochloric acid).
It makes up 1 or 2 parts per million of the Earth’s crust by weight. It is usually found in minerals such as columbite, tantalite, and coltan.
It is hard, rare, and highly corrosion-resistant, which makes it the perfect material for high-performance capacitors. It is also used in surgical instruments and body implants due to its ability to bond directly with hard tissue inside the human body.
In fact, it has been used by NASA to shield components of Voyager 1, Voyager 2, and other spacecraft from space radiation. Due to its impressive oxidation resistance and high melting point, it is used to build vacuum furnace parts, valve bodies, and thermowells.
Moreover, it is occasionally used in luxury watch brands, including Panerai, Omega, Hublot, and Journe.
A billet of enriched uranium
Density: 19.1 g/cm3
Like thorium, Uranium is weakly radioactive. It is naturally found in three isotopes: uranium-238, uranium-235, and less common uranium-234. While it occurs in low concentrations in rock, water, and soil, it is commercially extracted from uranium-bearing minerals like uraninite.
The existence of such an element was first discovered in 1789; however, its radioactive properties were discovered only in 1896 by Eugène-Melchior Péligot, and its practical use was done for the first time in 1934 after the Manhattan Project.
The metal is denser than lead and tantalum but slightly less dense than gold and tungsten. Due to its unique properties, it is widely used in high-density penetrators in the military sector.
Depleted uranium (which is less radioactive) can be alloyed with other metals like molybdenum or titanium so that it can be used as a shielding material to store and transport radioactive substances.
Although depleted uranium is less radioactive, it is dense enough to halt radiations from strong sources like radium. And since it can be machined and cast with ease at a relatively low cost, it is preferred over similarly dense materials.
Density: 19.25 g/cm3
Tungsten is obtained from rare minerals like scheelite and wolframite. It was first identified as an element in 1781 and classified as a metal in 1783.
Tungsten has the highest melting point (except carbon), highest tensile strength, and highest boiling point of all known elements. While pure single-crystalline tungsten is ductile and can be cut with harder metal, polycrystalline tungsten is intrinsically brittle and hard to work.
Its most common applications include X-ray tubes, incandescent light bulb filaments, welding electrodes, radiation shielding, and superalloys. A few tungsten compounds are used as catalysts to produce industrial chemicals.
Recently, tungsten has become popular in the 3D printing industry. Tungsten carbide is used to build 3D printer nozzles. Its high thermal conductivity and wear resistance enhances the printing quality of abrasive filaments.
Moreover, Metallic tungsten is utilized in jewelry as an alternative to platinum or gold. Since it is harder and causes fewer allergic reactions than gold alloys, it can be used to make rings, necklaces, and bangles with brushed finishes.
At present, the largest producer of tungsten is China (66,000 metric tons every year), followed by Vietnam (4,500 metric tons) and Russia (2,400 metric tons).
Gold-Coated James Webb Space Telescope
Density: 19.30 g/cm3
Gold is one of the most precious, popular, and sought-after materials on Earth. It has been used for jewelry, coinage, and other arts throughout history.
As per various studies, gold originated from supernova nucleosynthesis and from the collision of neutron stars in distant space.
On Earth, it is found in natural rocks formed billions of years ago. It mostly occurs as tiny (microscopic) particles embedded in rock, typically together with sulfide minerals or quartz. Earth’s oceans also contain very small amounts of gold — there are approximately ten grams of gold for every one billion metric tons of ocean water in the Atlantic and North Pacific.
Since gold has high resistance and electrical conductivity, it is used to make electrical connectors for all types of computerized devices. It is also used for the production of colored glass, tooth restoration, and infrared shielding.
Like all other metals, the density of gold decreases as it gets hotter. At just below its melting temperature (1064 °C), its density reduces to 18.31 g/cm3. At just above this temperature, the density of molten gold reduces to 17.19 g/cm3.
Have you ever wondered why you always get impure gold whenever you buy jewelry? Well, that’s because pure (24 carats) gold is soft. To make it more durable and strong, other metals like copper and silver are added, so it becomes impure in the process.
When gold is alloyed with other metals, the overall density of the alloy is reduced. The 18-carat gold with an equal proportion of copper and silver has a density of 15.4 g/cm3, while 9-carat gold has a density of 11 g/cm3.
According to Statista, the United States has approximately 3,000 metric tons of gold reserves in mines. Australia has the largest share of the world’s gold mine reserves. It accounts for 11,000 metric tons of gold, followed by Russia (6,800 metric tons).
Gold reserves (metric tonnes):
United States: 8,133
Saudi Arabia: 323
United Kingdom: 310
— World of Statistics (@stats_feed) May 6, 2023
Exposed Plutonium (pyrophoricity)
Density: 19.85 g/cm3
Plutonium is the densest radioactive element on Earth. It was first isolated in a University of California lab in 1940 when researchers detonated the uranium-238 in a huge Cyclotron.
Plutonium has a total of seven allotropes, whose densities range between 16 to 18.6 g/cm3.
Contrary to most of the elements in the periodic table, plutonium’s density increases by 2.5% when it melts. The density of the molten plutonium, however, decreases with temperature. Near its melting point, it has a relatively high viscosity and surface tension than other metals.
On a large scale, this deadly element was first used in the Manhattan Project — a substantial amount of plutonium was used to detonate a nuclear weapon (named “Fat Man”) in Nagasaki, Japan. After World War II, its use was solely restricted to producing commercial nuclear energy.
Today, about 35% of the energy generated in nuclear power plants comes from plutonium. It is formed in nuclear power reactors from uranium-238 as a by-product.
The isotope plutonium-238, in particular, emits a massive amount of thermal energy with low levels of neutron rays and gamma rays. One kilogram of plutonium-238 can produce nearly 570 watts of heat. That’s why it is used to power critical devices that must operate for 50-70 years without maintenance, such as spacecraft.
Rhenium is found in abundance in Molybdenite
Density: 21.2 g/cm3
Named after the river Rhine in Germany, Rhenium was discovered by three German scientists in 1925. It has the highest boiling point, except for carbon and tungsten. It also has the highest boiling point and third-highest melting point of any stable element at 5596 °C.
As one of the densest elements on Earth, it has a hexagonal, close-packed crystal structure. At normal temperature and pressure, it doesn’t react with nitric acid, hydrochloric acid, sulfuric acid, aqua regia, and alkalis.
Rhenium doesn’t occur freely in nature. It is extracted from porphyry molybdenum deposits and other minerals, usually in very low concentrations, averaging 0.001 parts per million.
Like other platinum group metals, rhenium is a precious Earth element, and its alloys are unique, with high melting points and impressive mechanical properties.
Due to these unique properties, rhenium alloys are used in exhaust nozzles and turbine blades of jet engines. It is also used as a catalyst for isomerization and hydrogenation. Moreover, molybdenum-rhenium and tungsten-rhenium alloys are utilized in heating elements, welding rods, semiconductors, metallic coatings, and X-ray anodes.
Density: 21.45 g/cm3
Platinum is one of the rarest Earth metals, with an average abundance of 5 micrograms per kilogram. It is found in Earth’s crust as native deposits and in some copper and nickel ores.
The element is also one of the least reactive metals that exhibits excellent corrosion resistance even at high temperatures. Since it doesn’t react with other materials under high temperatures and pressure, it is often found as native platinum.
Although it remains unaffected by water and air, it dissolves in hot, concentrated sulphuric and phosphoric acids and hot aqua regia.
Despite being dense, pure platinum is soft and can be easily damaged (just like gold). That’s why it is hardened by mixing with other metals like palladium, ruthenium, rhodium, and iridium. Platinum-ruthenium alloy, for example, has a bright luster and doesn’t tarnish.
Besides jewelry, Platinum is used in vehicle emissions control devices, dentistry equipment, laboratory equipment, electrodes, catalytic converters, and turbine engines.
About 80% of the total platinum is produced in South Africa. The country produces 130 metric tons every year. Russia comes in a distant second place, with an annual production capacity of 19 metric tons.
Density: 22.56 g/cm3
Iridium is the second-densest element and one of the rarest elements in Earth’s crust. It was discovered in 1803 in residues of platinum ores by an English chemist, Smithson Tennant.
It has two naturally occurring, stable isotopes: Iridium-191 and Iridium-193. Additionally, over 37 radioisotopes have been synthesized to date.
Iridium also has the most corrosion-resistant property of any metal, even at extreme temperatures near 2,000 °C. At normal temperature and pressure, it is not affected by bases, acids, or most strong chemicals. These properties make iridium a valuable transition metal.
Since iridium is eight times stronger and six times harder than platinum, it is primarily used to make high-performance spark plugs. While copper spark plugs can last 20,000 miles, platinum electrodes have a life expectancy of about 100,000 miles, and iridium spark plugs can last 25% longer than that.
It can also be used as electrodes for the production of chlorine (in the Chlor-alkali process) and as crucibles for the recrystallization of semiconductors at high temperatures.
Moreover, the current display technology, specifically OLED screens, uses iridium compounds to produce light and vibrant colors.
Density: 22.59 g/cm3
Osmium is the densest naturally occurring element on Earth. It is also among the rarest elements, making 50 parts per trillion of the Earth’s crust.
This gray-white metal is twice as dense as lead. It is very hard and brittle and has the fourth-highest melting point of all elements (after carbon, tungsten, and rhenium). Its bulk modulus is extremely high, ranging from 395 to 462 GPa, which is comparable to that of diamond.
These properties make osmium difficult to machine, form, or work, even at high temperatures.
While pure osmium doesn’t occur in nature, its native alloys are found with platinum metals. It was first discovered in 1803 by Smithson Tennant. He discovered the element together with iridium in the residues of platinum ores that are insoluble in aqua regia.
Due to the extreme toxicity and volatility of osmium oxide, the element is rarely used in its pure form. It is usually alloyed with other platinum-group metals for high-wear applications. These alloys are used to make tips for fountain pens, electrical contacts, and instrument pivots.
More to Know
What is the densest naturally occurring material on Earth?
Osmium is Earth’s densest naturally occurring material, having a density of 22.59 grams per cubic centimeter. It is found naturally in the Earth’s crust, typically along with other platinum group elements.
Osmium’s high density can be attributed to its atomic structure. It has a very dense atomic nucleus and a relatively large number of protons and neutrons packed within its nucleus, which leads to a high atomic mass.
It also has an exceptionally high melting point of about 3,033 degrees Celsius. This is due to the strong metallic bonds in its crystal lattice.
Importance of Density in Materials Science
Density is not just a number — it underpins the characteristics and application of materials. It’s an important parameter in materials science for several reasons:
- It helps scientists distinguish one material from another
- It can significantly impact the performance of a material
- It allows scientists to analyze phase changes and study material’s behavior under varying conditions
Engineers select materials based on their density, ensuring that the product meets its intended performance requirements. High-density materials, for instance, may be used for their strength and durability, while low-density materials are preferred for their buoyancy or lightweight properties.
Materials with unusual or surprising density characteristics
Some materials or bodies have very strange density characteristics. For example
- Aerogels have extremely low densities (as low as 0.001 g/cm³)
- Pykrete has an unusually low density for a solid (about 0.9 g/cm³)
- Black Holes have an extremely high (or theoretically infinite) density
Is diamond the hardest material found on Earth?
No, it isn’t. Researchers have discovered six materials that are harder than diamonds. These include Graphene, Buckypaper, Palladium microalloy glass, Dyneema, Lonsdaleite, and Wurtzite Boron Nitride.
In proportion to thickness, graphene is the strongest material known to humans. It’s a single layer of carbon atoms tightly bound in a hexagonal lattice nanostructure. It has an exceptional intrinsic tensile strength of 19,000,000 psi and Young’s modulus of close to 150,000,000 psi.
What’s the most expensive liquid in the world?
Onasemnogene abeparvovec is currently the most expensive medication available in liquid form. It is used to treat a rare neuromuscular disorder called spinal muscular atrophy. A single dose (5.5 mL) costs US$ 2.125 million.