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Bohrium has not been isolated in pure form, and its properties have not been conclusively observed; only manganese, technetium, and rhenium have had their properties experimentally confirmed. All three elements are typical silvery-white transition metals, hard, and have high melting and boiling points.
Group 7 contains the two naturally occurring transition metals discovered last: technetium and rhenium. Manganese has been known for millennia. Rhenium was discovered when Masataka Ogawa found what he thought was element 43 in thorianite, but this was dismissed; recent studies by H. K. Yoshihara suggest that he discovered rhenium instead, a fact not realized at the time. Walter Noddack, Otto Berg, and Ida Tacke were the first to conclusively identify rhenium; it was thought they discovered element 43 as well, but as the experiment could not be replicated, it was dismissed. Technetium was formally discovered in December 1936 by Carlo Perrier and Emilio Segré, who discovered Technetium-95 and Technetium-97. Bohrium was discovered in 1981 by a team led by Peter Armbruster and Gottfried Münzenburg by bombarding Bismuth-209 with Chromium-54.
Manganese is the only common Group 7 element. In 2007 11 million metric tons of manganese were mined. All other elements are either incredibly rare on earth (technetium, rhenium) or completely synthetic (bohrium). In contrast to manganese, only 40 or 50 metric tons of rhenium were mined. Technetium is only found in trace amounts in nature as a product of spontaneous fission; almost all is produced in laboratories. Bohrium is only produced in nuclear reactors and has never been isolated in pure form.
Only manganese has a role in the human body. It is an essential trace nutrient, with the body containing approximately 10 milligrams at any given time, being mainly in the liver and kidneys. Many enzymes contain manganese, making it essential for life, and is also found in chloroplasts. Technetium, rhenium, and bohrium have no known biological roles. Technetium is however used in radioimaging.