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Chrysanthemum Stone
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In Cheongsong area, very rare spherulitic rhyolites both in Korea and foreign
countries occur as dykes showing various types. The spherulites in them
represent an undercooling caused by very fast cooling of the dykes in a shallow
depth near to the surface and the variety of types were resulted from the
difference of relative cooling rate. Cheongsong spherulitic rhyolites can be
classified into five types based on the cooling rate; radiated simple
spherulite, layered simple spherulite, layered multiple spherulite,
radiated-layered multiple spherulite, radiating layered multiple spherulite.
Radiated simple and radiating layered multiple spherulites formed by diffusion
current caused by undercooling related to very fast cooling. On the other hand,
layered multiple spherulites formed by relatively slow diffusion as a Liesegang
ring during relatively slow cooling. If the cooling rate is between the two
cases, layered simple spherulites formed. This interpretation indicates that
Chrysanthemum, Dahlia and Sunflower types which are included in radiated simple
or radiating layered multiple spherulite formed in the dykes with the fastest
cooling rate in Cheongsong area while Peony, Rose and Innominate types
classified as layered multiple spherulite formed in the dykes with the
relatively slowest cooling rate. At the cooling rate between them, Apricot type
spherulites formed. The K-Ar age-dating for Cheongsong spherulitic rhyolites
indicate then to be formed between 48 and 50 Ma. The Cheongsong rhyolites are
very valuable for research and preservation because of their rarity, beauty and
diversity.
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