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Hokutolite is also known as lead-rich baryte and is a compound of lead sulfate (PbSO4) and barium sulfate (BaSO4). It is mildly radioactive due to the presence of radioactive elements such as radium (Ra), iodite (Io), polonium (Po) and bismuth (Bi). It is named after the Japanese name for Beitou in Taiwan and is the only mineral to be named after a Taiwanese location. The only known sources of Hokutolite in the world are river valleys in Akita Prefecture in Japan and the Beitou River in Taiwan. Hokutolite is formed through the crystallization of hot spring sediments. Hardness is between 3.0 and 3.5, has a specific gravity between 4.69 and 4.93, and the color ranges from milky white to yellow-ochre. It usually grows on jarosite or opaline silica and its formation is closely related to the temperature, composition and volume of hot spring waters. 

Mineral Formation
Mainly forms on the surface of riverbed pebbles or in the spaces between pebbles below the hot spring. It grows on the outermost layer of the crust formed by hot spring sediments and has a thickness of just a few centimeters. The crystals are small, rhombohedral in shape and finely spaced. Hot spring sediments, with the exception of hokutolite, are usually yellow-ochre jarosite. 
Geographic Distribution
Lower reaches of the geothermal valley of Beitou River in Taipei City. 
Mining History
Hokutolite was initially discovered by the Japanese geologist Yohachiro Okamoto in 1905 on the riverbed of Beitou River. During a geological survey of the Beitou River, Okamoto placed the photo film he had taken on a rock in Beitou River. When he arrived at home he discovered that the film had already been exposed. He sent the rock to Tokyo for testing and it was found to contain the radioactive element Radium which caused the film to become exposed. In 1912 Professor Kotora Jimbo submitted the new discovery at an international mineralogy conference. As it was found at the Beitou River in Taiwan, it was officially named "Hokutolite".  Hokutolite was designated a "Natural Monument" in 1933 and a mining ban imposed. To commemorate Okamoto's contribution to the study of Hokutolite, the "Okamoto Honor Stele" was built in 1940 and can be seen today at the Shanguang Temple in Beitou. 
(1) Academic research.
(2) Specimen collection.
Chemical Composition
tr: Rare
Source: P.Y. Chen et al. (2004).

Hokutolite Conservation
The formation of Hokutolite depends on very exact environmental factors. The flow rate, composition, temperature and pH value of the water all affects its growth. In Japan, "Hokutolite" has been designated a "Special Natural Monument" and mining is banned by law. In Taiwan, hokutolite was illegally collected from the Beitou River for many years. The destruction of the environment and water pollution means that the environment is no longer conducive to the growth of hokutolite so new formations are now extremely rare and it is now protected by law.  
In 1998 the "Beitou Hot Spring Museum" was opened and features not only exhibits on Beitou's geography, history, industry, culture and different hot spring sources but also hokutolite specimens, its formation and composition, and also a hokutolite radioactivity lab available by request. In 2000 an Executive Yuan cultural task force designated hokutolite as a "Natural and Cultural Sight". A "Beitou River (Hokutolite) Natural Reserve" was also set up, making it the first mineral in Taiwan to be designated for preservation.

National Museum of Natural Science