The rarest gemstone on Earth is kyawthuite, a transparent orange-red mineral weighing just 0.3 grams, with only one specimen discovered in Myanmar, currently housed at the Los Angeles Natural History Museum.
Unique items are often human-made rather than a natural mineral specimen from Earth. Humans inhabit a vast planet, so if geological processes create a type of mineral in one location, it’s likely they produce something similar in another. Among the 6,000 minerals recognized by the International Mineralogical Association, many form from various chemical processes but yield similar results.
The only specimen of kyawthuite. (Photo: Los Angeles Natural History Museum)
Even if a mineral forms only once, the specimen can easily break and scatter across a wide area. Therefore, with only one recorded specimen, kyawthuite crystals are quite remarkable.
Sapphire hunters found the kyawthuite specimen beneath a stream near Mogok, Myanmar. It exists as a gemstone and was recognized by the International Mineralogical Association in 2015. The scientific description of kyawthuite was published in 2017. The Los Angeles Natural History Museum currently holds this unique specimen.
After collecting the mineral specimen from the Chaung-gyi valley, experts cut it into a 1.61-carat gemstone for study. The research process revealed that it likely formed deep within the Earth in the form of pegmatite rock, with asymmetric structure and a hardness of 5.5 on the Mohs scale, according to IFL Science. Hardness and durability are two different characteristics of gemstones. Hardness refers to scratch resistance, while durability relates to breakage resistance. The minerals containing gemstones are the result of the Earth’s continuous activity. The processes of collision, fracturing, heating, and cooling of tectonic plates provide the conditions for gemstone formation.
Kyawthuite is transparent orange-red and the specimen weighs 1.61 carats (0.3 grams). Its chemical formula is Bi3+Sb5+O4, with a trace of tantalum. Both bismuth (Bi) and antimony (Sb) are rare metals, but not extraordinarily uncommon. The amount of bismuth in the Earth’s crust exceeds that of 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 its formation process, not due to a shortage of its constituent elements.
Bismuth is so dense that the specific gravity of kyawthuite is eight times that of water and double that of ruby, a gemstone somewhat similar to kyawthuite. Thus, the kyawthuite specimen is actually smaller than what one might imagine based on its weight.
The mineral database of the California Institute of Technology (Caltech) describes the structure of kyawthuite as consisting of Sb5+O6 octahedral sheets arranged parallel to Bi3+ atoms. This is currently the only recognized bismuth-antimony oxide. The mineral is named after Dr. Kyaw Thu, who was a geologist at the University of Yangon, Myanmar.
Myanmar is home to many rare minerals, including jadeite and the second rarest mineral in the world, painite. In addition to these, borate minerals are also known from only a few specimens, which are dark red and were first discovered by British mineralogist Arthur Pain.
