See also Potassium chloride and chloride
Potassium is an element<ref>Wile, Dr. Jay L. Exploring Creation With Physical Science. Apologia Educational Ministries, Inc. 1999, 2000</ref> in the alkali metals class of the periodic table. It is so chemically active that it is never found free (in elemental form) in nature. In its elemental form, it reacts with water, forming potassium hydroxide and hydrogen gas, so violently that the hydrogen usually catches fire. It reacts with the halogens to make halides like potassium chloride.
Its existence as “potash” or “vegetable alkali” (potassium carbonate), “caustic potash” (potassium hydroxide), etc., had long been known, but it was not isolated as an element until 1807, by Sir Humphrey Davy. It was isolated by electrolysis of potassium hydroxide.
The radioactive decay of potassium provides a method of radiometric dating called potassium-argon dating that is used to calculate the ages of volcanic rocks.