The rock found in the lower stream of Beitou Stream 北投溪 is unusual in many ways, It is a heavy rock with the compositions of both barium sulfate and lead sulfate with a hardness of 3.0~3.5 and specific gravity of 4.69~4.83. When a Japanese geologist Mr. Yohachiro Okamoto 岡本要八郎 came to Beitou in 1906 to collect the rock, he immediately saw the differences of this rock from all other rocks he knew from the textbook. Mr. Yohachiro Okamoto published his research finding in Tokyo, Japan in 1911. Next year, his advisor, Dr. Kotora Jimbo 神保小虎published Okamoto's finding in Europe and named the rock as Hokutolite or 北投石; the academic position of Hokutolite was then established.
Beitou Stream is a hot spring stream. The water temperature of the stream at the originated place is around 70 degrees centigrade. At the lower stream, the temperature drops to around 30 degrees centigrade. The minerals begin to crystallize at the lower stream; crystallization conditions will depend on pH, water contents and water temperature. The crystals of hokutolite mainly consists of solid solutions of barium sulfate BaSO4 and lead sulfate PbSO4. It also contains radiactive substance, radium element.
In 1962, Dr Lee Yueon-Jeh 李遠哲, the only Taiwanese Nobel Laureate wrote a master-degree thesis on the radioactivity studies of hokutolite while he was still at Ching-Hua University 请華大学.
Photo shows a sample of hokutolite.
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