Thorium dioxide
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Thorium dioxide, also called thorium oxide or thoria, is a crystalline solid, often white or yellow in colour. Thorianite is the name of the mineralogical form of thorium dioxide. It is moderately rar
Yellowed thorium dioxide lens (left), a similar lens partially de-yellowed with ultraviolet radiation (centre), and lens without yellowing (right)
Thorium
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Thorium is a chemical element; it has symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive grey when it is exposed to air, forming thorium dioxide;
Thorium dioxide
…also called thorium(IV) oxide or thoria, is a crystalline solid, often white or yellow in colour. Thorianite is the name of the mineralogical form of thorium dioxide. It is moderately rare and crystallizes in an isometric system. The melting point of thorium oxide is 3300 °C – the highest of all known oxides…
A thin square of thorium metal in a glass ampoule
Thor's Fight with the Giants (1872) by Mårten Eskil Winge; Thor, the Norse god of thunder, raising his hammer Mjölnir in a battle against the giants.
Jöns Jacob Berzelius, who first identified thorium as a new element
World War II thorium dioxide gas mantle