Gold is not the rarest but a rare metal. But, why is gold rare? Its rarity along with its noble nature has made it expensive. Apart from this, it is widely used in jewellery because of its malleability i.e. a single gram of gold can have a meter square wide sheet.
These properties make gold expensive. Had it not been rare, it might not have been so expensive. In order to discern the cause of its rarity, let us first know what makes things rare?
Rarity of materials
The rarity of a material is the measure of the quantity of it present in the universe. The materials which are made in less proportion in the universe are termed rare. So, the rarity of materials reflects that it is forged less in the universe. To know the reason that they are produced less, we have to know about the abundance of other materials.
Everything is made up of atoms and every atom is made up of protons, electrons, and neutrons. A material is considered simple if it is made up of a few such particles. Mostly, simplest materials are abundant in the universe such as Hydrogen and helium.
Hydrogen contains one proton and one electron while helium contains 2 protons, 2 neutrons, and 2 electrons. This makes them the simplest of all elements and the most abundant in the universe. The complex ones are hard to be manufactured and hence less in proportion.
Our Universe contains mostly hydrogen and helium whereas other materials are forged from them. The heavier materials other than hydrogen and helium are forged in the heart of the dying stars during the supernova explosion.
Inside a dying star, the helium and hydrogen can combine to form more heavier elements and finally during supernova explosion much heavier elements can be produced.
Since dying of stars is rare, heavier elements are formed rarely. As a result, the quantity of those elements is less in comparison to hydrogen and helium. Other processes that can result in the formation of such materials is the collision of stars, which is still too rare.
Why is gold rare?
Gold is the element with atomic number 79. It has 79 protons, an equal number of electrons and 118 neutrons. This makes gold one of the heavy elements. If hydrogen and helium were to combine to form gold, they have to combine into many other heavier elements before finally resulting in gold.
The gold that exists in the universe was believed to have originated from the supernova explosions but a recent study has shown that most of the universe’s gold is created by neutron star merger.
A neutron star merger can be responsible for the production of elements heavier than iron as discovered by the recent observation of a neutron star merger. Usually, elements heavier than iron are not likely to form in a supernova explosion.
However, these explosions and collisions that are responsible for manufacturing gold are rarer in the universe. Their rare nature results in less amount of gold to be produced. But still, that does not explain the gold that is found on Earth. Why is gold rare on Earth?
Earth’s gold hypothesis
So far the origin of the gold is responsible for the rareness of gold and other heavy elements in the universe. As we consider Earth, the gold on Earth is believed to be deposited from the formation of Earth.
The gold originated from such explosions and collisions were present in the dust from which solar system was formed. This gold remained in the heavy core of the Earth and inside the mantle.
During large asteroid impact, the gold came to the surface. Since the forging of gold needs an ample amount of energy, it is the only hypothesis we are left with.
Gold is the most malleable and one of the noble material (resistant to corrosion). The heavy materials as gold were formed in the exploding stars and during the collision of neutron stars.
The heavier elements remained in the gaseous form and finally merged during the formation of the solar system. Since these materials need a lot of energy to be forged, they are very less in proportion in the universe and hence rare.