486 mckelvey. SEDIMENTARY MINERAL DEPOSITS [Ch. 27 



TABLE 1 



Value of 1946 Domestic Mineral Production Classified by Rock Type 1 



Percent 

 of 

 Value Total 



Igneous rocks (including granite, basalt, pegmatite min- 

 erals, chromite, etc.) $ 57,800,000 1 



Sedimentary rocks (see Table 2) 2,690,000,000 36 



Metamorphic rocks (including slate, marble, quartzite, 

 anthracite coal, garnet, etc.) 447,000,000 6 



Veins, disseminations, and replacement bodies (includ- 

 ing salt-dome sulphur and salt, most contact-meta- 

 morphic deposits, sandstone vanadium and uranium 

 ores, asphalt, gilsonite, and related bitumens, as well 

 as the bulk of the metalliferous deposits) 493,000,000 6 



Residuum (including kaolin and bauxite, Lake Superior 

 iron ores and manganiferous iron ores, most domestic 

 .manganese ores, many barite deposits, mineral pig- 

 ments, Tennessee and Florida hardrock phosphate 

 deposits, etc.) 218,000,000 3 



Fluids (including petroleum, natural gas, sea water, 

 brines, etc.; surface and ground water are not in- 

 cluded, but only because their value is unknown) 3,590,000,000 48 



Total $7,500,000,000 100 



1 Although the rocks of the earth's crust are customarily divided into three main 

 classes — igneous, sedimentary, and metamorphic — it has long been recognized that 

 many earth materials, such as residual and supergene ores, talus, landslides, veins, 

 and water, are not so classifiable (see Ashley et al., p. 428). Although the volume of 

 most of these materials (water is a prominent exception) is much less than that of the 

 three principal rock types, they are of equal, if not greater, importance economically 

 and deserve recognition as separate rock types in any scheme of classification of 

 mineral deposits. The additional rock classes presented in this table are provisional. 

 Admittedly they all are not sharply definable (this characteristic they share with 

 the traditional classes, however), and, whereas the traditional classes are defined 

 genetically, two of the classes used here (veins, etc., and fluids) are defined descrip- 

 tively. The only defense and recommendation offered for this classification is that 

 it does allow a more simple and yet geologically significant classification of minerals 

 (used in the broad sense, as "mineral production" or "mineral resources") actually 

 produced than any other classification known to me. 



The values for the individual minerals and rocks are not strictly comparable or 

 accurate. As explained in the Statistical Summary of Mineral Production in the 

 U. S. Bureau of Mines Minerals Yearbook, from which the data have been compiled, 

 some production figures represent the value of the crude materials; some are re- 

 ported only for refined materials; and some are reported only for the finished product 

 (such as cement). In this compilation, the production figures totaled are of the 

 crude material or the crudest form of the product for which figures are available. 

 As many minerals are mined from more than one class of rock, it is difficult to tell 

 from the general production figures available how much of the production of a given 

 mineral comes from rocks of one class and how much from another. In addition, 

 the uncertain origin of many minerals makes their classification difficult. Many of 

 the errors introduced by these uncertainties should be compensating, however, and 

 the totals are probably valid as to order of magnitude. D. F. Davidson assisted in 

 tabulation of the data. 



