16 



most extensively mined throughout the world.^^ It forms the back- 

 bone of the construction industry as aggregate and filler material. 

 Smaller percentages go into glassmaking and other relatively minor 

 industries. 



Although most of the sand and gravel is mined at or near the 

 beaches, the ever-increasing populations and their concentration in 

 coastal areas create demands that are expected to push this industry 

 into the offshore areas.^' Construction being essential to accommodate 

 these demands, the seabed will increase in value for providing the 

 necessary sand and gravel aggregate for the future. 



Calcium carbonate shells and sands fragmented from them are also 

 mined for use in the production of portland cement and lime. Oyster 

 shells and other calcareous shell deposits are mined from several 

 coastal locations in the United States and elsewhere in the world.^* 



HEAVY MINERALS 



Several minerals occur in association with, or under, the beach sands 

 overlying the bedrock. These minerals, referred to as heavy minerals,^^ 

 are now mainly derived from sources on land. As the rocks on land 

 undergo the relentless battering of wind, rain, ice, and other destruc- 

 tive agents, the rocks yield to the processes of chemical and mechanical 

 weathering. The weathered fragments are transported by streams and 

 wind to their final destination in the sea. There, the winnowing action 

 of the waves serves to concentrate the heavier minerals and metals into 

 profitably minable deposits. 



As would be expected, the heavier the mineral the closer to shore it 

 is deposited. Consequently, these placer deposits are expected to be 

 located on present beaches, on submerged beaches, and a few miles 

 offshore, near their source rocks on land. They usually include the 

 heavier metals like gold, tin, and platinum, and the relatively lighter 

 minerals like diamond, the titanium minerals ihnenite and rutile, the 

 tungsten minerals scheelite and wolframite, the iron ore magnetite, 

 chromite, and zircon. 



Although seabed placer deposits are normally not as abundant nor as 

 valuable as their counterparts on land, several exceptions are found 

 around the world such as the tin deposits off the coast of Cornwall in 

 England and off the coast of Indochina, the diamond deposits off 

 the coast of southwest Africa, and the zircon sands of New South 

 Wales, Australia. 



PHOSPHORITE 



Among the mineral deposits on the seabed, phosphorite has been 

 found in extensive areas of the continental margin, and appears to 

 have a promising potential for the mining industry. Phosphate 



'« Current production in the United States exceeds 50 million cubic yards. 



"John Schlee of the U.S. Geological Survey estimates that 50,000 square miles of the 

 continental shelf off New England, Long Island, and New Jersey are blanketed with sand 

 and gravel. A large deposit off the New Jersey coast lies in 66 to 132 feet of water and 

 may contain several billion tons of gravel. 



18 Offshore production of oyster shells exceeds 20 million tons annually. 



1" Minerals are separated from a mixture of crushed rock in a liquid called "bromoform," 

 Bromoform has a specific gravity of 2.85 ; minerals with specific gravity greater than that 

 of bromoform are referred to as heavy minerals. 



