Chemical element chemical bonds, they form chemical compounds. Only a minority of elements are found uncombined as relatively pure minerals. Among the more common of such native elements are copper, silver, gold, carbon (as coal, graphite, or diamonds), and sulfur. All but a few of the most inert elements, such as noble gases and noble metals, are usually found on Earth in chemically combined form, as chemical compounds. While about 32 of the chemical elements occur on Earth in native uncombined forms, most of these occur as mixtures. For example, atmospheric air is primarily a mixture of nitrogen, oxygen, and argon, and
CU convoys CU 23, CU 24, CU 28, CU 30, CU 33, and CU 35 included troopships and are sometimes identified with a TCU prefix. Convoy CU 24 sailed in two sections with troopships in TCU 24A and ammunition ships in TCU 24B. A total of 2255 ships crossed the Atlantic in CU convoys until convoy CU 73 made the last departure from New York on 30 May 1945. Submarines sank three loaded United States tankers from CU convoys: Empty ships travelling westbound on similar routes were designated UC convoys. Seventeen ballasted tankers departed from Liverpool on 15 February 1943 as convoy