The only specimen of Earth's rarest mineral

The rarest gemstone on Earth is kyawthuite, a 0.3-gram transparent orange-red mineral of which only a single specimen has been found in Myanmar, and is now at the Natural History Museum of Los Angeles.

Unique things are often man-made, not a natural sample of Earth minerals. We live on a big planet, so if geological processes create a mineral in one place, they are likely to create the same one in another. Of the 6,000 minerals recognized by the International Mineralogical Association, many are formed by different chemical processes that lead to the same result.

The only specimen of kyawthuite. (Photo: Los Angeles Museum of Natural History)

Even when the mineral forms only once, specimens can easily break and be scattered over a large area. Therefore, with only one specimen ever recorded, the kyawthuite crystal is remarkable.

Sapphire hunters found a specimen of kyawthuite in a stream near Mogok, Myanmar. It exists as a gemstone and was recognized by the International Mineralogical Association in 2015. A scientific description of kyawthuite was published in 2017. The Natural History Museum of Los Angeles is currently home to the only specimen.

After collecting a sample of the mineral from the Chaung-gyi Valley, experts cut it into a 1.61-carat gemstone for study. The study revealed that it most likely formed deep underground as a pegmatite , an asymmetrical rock with a Mohs hardness of 5.5 , according to IFL Science. Hardness and durability are two different characteristics of gemstones. Hardness refers to the ability to resist scratches while durability refers to the ability to resist breakage. Gemstone-containing minerals are the result of the Earth's constant activity. It is the process of tectonic plates colliding, breaking, heating, and cooling that provides the conditions for gemstone formation.

Kyawthuite is a transparent orange-red color and the specimen weighs 1.61 carats (0.3 grams). The chemical formula is Bi ₃ +Sb ₅ +O ₄ , with a trace of tantalum . Both bismuth (Bi) and antimony (Sb) are rare metals, but not unusual. Bismuth is more abundant in the Earth's crust than gold, while antimony is more abundant than silver. Oxygen is the most abundant element in the Earth's crust. Therefore, the rarity of kyawthuite is related to the formation process , not to a lack of constituents.

Bismuth is such a heavy element that kyawthuite is eight times more dense than water and twice as dense as ruby, a gemstone it is somewhat similar to. As a result, kyawthuite specimens are actually smaller than one might expect from their weight.

The California Institute of Technology (Caltech) Mineral Repository describes the structure of kyawthuite as a grid of Sb5+O6 octahedra arranged parallel to the Bi3+ atoms. It is currently the only recognized bismuth-antimony oxide . The mineral is named after Dr. Kyaw Thu, a former geologist at Yangon University, Myanmar.

Myanmar is home to many rare minerals, including jade and the world's second rarest mineral, painite. In addition, borate, known only from a few specimens, is a deep red mineral first discovered by the British mineralogist Arthur Pain.