Most people appreciate the beauty of quartz, possibly without knowing that it is actually the most common mineral on our planet. In the world of minerals, rarity usually lies in the hands of humans, crafted through clever processes and creativity.
There are currently 6,000 minerals recognized by the International Mineralogical Association (IMA). Many of them are formed by multiple processes, with different chemistry that lead to identical outcomes. However, there exists an exception to this rule, where nature itself has fashioned a unique masterpiece.
Rarest Mineral on Earth
Minerals are scattered everywhere on Earth, from flecks in sand or gravel to actual hidden gems. According to the US Geological Survey, minerals refer to naturally occurring elements or compounds which do not contain carbon (inorganic). Every type of mineral exhibits order in its internal structure and has a unique chemical composition.
The rarest mineral on our planet is kyawthuite, a natural form of bismuth antimonate. Only one crystal of this mineral is known to exist, found in the Mogok region of Myanmar.
The precious stone was originally found by gem prospectors in Chaung Gyi village called "Ruby Land", a part of the Mandalay region in Myanmar. The finders, not realizing the raw stone's uniqueness, set it out for sale at a market. This is where it was found by Dr. U Kyaw Thu, a former geologist at Yangon University.
From his experience in the field and in buying stone from the Khanae market, U Kyaw Thu could tell that this stone was a little strange, so he decided to buy it in 2010. He took the gem with him at Yangon city where it was examined and determined as not like any other gem they have ever found.
Confirming the rarity of the stone was difficult in Myanmar, so U Kyaw Thu collaborated with experts from the US and the International Mineralogical Association. In December 2015, IMS recognized it as the first ever of its kind discovered in the world. Today, the one and only specimen of this gem is kept at the Natural History Museum of Los Angeles City.
Even if a mineral only formed once, its samples can easily be broken up and scattered over a wide area. It is very unusual that any mineral would be known from just a single sample, but this is indeed the case for kyawthuite.
The chemical formula of kyawthuite is Bi3+Sb5+O4, with traces of tantalum. Bismuth and antimony are both rare metals, but not extraordinarily so. In the Earth's crust, there is also more bismuth than gold, while antimony is more abundant than silver. Meanwhile, oxygen is the most abundant element in the Earth's crust. This means that the rarity of Kyawthuite might be due to the way in which it formed, rather than the shortage of its ingredients.
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Physical and Chemical Properties of Kyawthuite
Mineral database from California Institute of Technology describes kyawthuite as a small (1.61-karat) deep-orange jewel. It has a hardness of 5 ½ in Mohs scale. It also has a specific gravity of 8.256 and adamantine luster, which means that it has a refractive index of 1.9 to 2.5.
Kyawthuite is the only approved Bi-Sb oxide mineral and could be a chemical analogue of clinobisvanite (BiVO4), but with slightly different space groups. This mineral is not analogous to bismutotantalite or bismutocolumbite. It is classified as monoclinic in the crystal system and is isostructural with clinocervantite.
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