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UNITED STATES MINERAL RESOURCES 



treatment. Many are mineral raw materials, others 

 are waste or synthetic products, and some are or- 

 ganic materials. A brief look at the array of ma- 

 terials and at some of their properties is given in 

 table 66. Several of the materials touched on in this 

 chapter are also discussed in other chapters. (See 

 "Abrasives," "Clays," "Diatomite," "Pigments and 

 Fillers," "Magnesian Refractories," and "Silica 

 Sand.") 



The distinction between normal-weight and light- 

 weight aggregates is made at about 75 lb per cu ft 

 (pounds per cubic foot) for loose graded aggregate. 

 Most lightweight aggregates weigh considerably 

 less; generally those used for structural purposes 



are in the 35- to 60-pound range and those used for 

 non-load-bearing purposes are in the 5- to 20-pound 

 range (ultralightweight aggregates). 



Expanded clays and shales make up more than 

 70 percent by weight of the structural lightweight 

 aggregates used annually, with the remainder di- 

 vided among expanded slate, scoria, expanded slag, 

 and fly ash at about 6, 7, 15, and 2 percent, respec- 

 tively. The production data for clays and shales are 

 commingled and cannot be separated satisfactorily, 

 but about half of all the aggregate seems to be 

 made from expanded shale. 



Vermiculite and perlite are the most used ultra- 

 lightweight materials, each with about one-third 



Table 66. — Classification and properties of lightweight aggregate materials 



