<P> Barite, a mineral containing barium, was first recognized as containing a new element in 1774 by Carl Scheele, although he was able to isolate only barium oxide . Barium oxide was isolated again two years later by Johan Gottlieb Gahn . Later in the 18th century, William Withering noticed a heavy mineral in the Cumberland lead mines, which are now known to contain barium . Barium itself was finally isolated in 1808 when Sir Humphry Davy used electrolysis with molten salts, and Davy named the element barium, after baryta . Later, Robert Bunsen and Augustus Matthiessen isolated pure barium by electrolysis of a mixture of barium chloride and ammonium chloride . </P> <P> While studying uraninite, on 21 December 1898, Marie and Pierre Curie discovered that, even after uranium had decayed, the material created was still radioactive . The material behaved somewhat similarly to barium compounds, although some properties, such as the color of the flame test and spectral lines, were much different . They announced the discovery of a new element on 26 December 1898 to the French Academy of Sciences . Radium was named in 1899 from the word radius, meaning ray, as radium emitted power in the form of rays . </P> <P> Beryllium occurs in the earth's crust at a concentration of two to six parts per million (ppm), much of which is in soils, where it has a concentration of six ppm . Beryllium is one of the rarest elements in seawater, even rarer than elements such as scandium, with a concentration of 0.2 parts per trillion . However, in freshwater, beryllium is somewhat more common, with a concentration of 0.1 parts per billion . </P> <P> Magnesium and calcium are very common in the earth's crust, with calcium the fifth-most - abundant element, and magnesium the eighth . None of the alkaline earth metals are found in their elemental state, but magnesium and calcium are found in many rocks and minerals: magnesium in carnallite, magnesite, and dolomite; and calcium in chalk, limestone, gypsum, and anhydrite . </P>

Where are alkaline earth metals found on earth