The sand-size quartz and feldspar grains in all samples in which they occur 

 were checked for surface frosting and pitting effects. Sand grains from the rela- 

 tively quartz-rich northwest basin are often strongly frosted, whereas frosting and 

 pitting is much less common on quortz grains found to the east of the ridge in the 

 southeast basin and on the Indian continental shelf. In Figure 10, samples in which 

 frosted grains were observed are designated by X's. 



F. Heavy Minerals 



The heavy mineralogy of the same eight samples analyzed for light minerals is 

 also shown in Table 1 . Heavy mineral suites from the Arabian coast do not seem to 

 differ fundamentally from those of the Indian shelf. All suites ore unstable and are 

 derived from both metamorphic and igneous rocks. Most of the mineral grains, in- 

 cluding mica, are fresh in appearance . 



Biotite shows more sample to sample variation than any other mineral, ranging 

 from 0.5 to 74.0 percent. In two samples, Nos. 51 and 89, biotite is by far the 

 most common heavy mineral (74.0 and 63.5 percent, respectively). In all samples, 

 biotite is more abundant than muscovite, but it is possible that some muscovite is 

 too light to be completely separated by treatment with tetrabromoethane . In sample 

 No. 51, muscovite and biotite together make up to 85 percent of the heavy minerals, 

 Along the Arabian coast, the biotite content apparently increases with distance from 

 shore - probably a function of wind and/or water sorting processes on the flat mica 

 grains . 



Epidote is also variable in concentration, ranging from to 23 percent. The 

 average concentrations of the major heavy minerals of all eight northern Arabian 

 Sea samples observed are: opaques, 17.7%; hornblende, 9.1%; tremolite-actinolfte, 

 13.0%; biotite, 23.6%; muscovite, 3.5%; olivine, 6.2%; garnet, 2.6%; epidote, 

 12.8%; rutile, 1 .0%; sphene, 3.5%; tourmaline, 4.1%; and zircon, 1 .4% . 



G. Cloy Mineralogy 



The general distribution of clay minerals from sediments of the study area is 

 delineated in Figure 11 . On the basis of the illite-chlorite-montmorillonite content, 

 three reasonably distinct clay mineral provinces can be distinguished: (1) a montmo- 

 rillonite-rich assemblage from sediments of the southeastern portion of the study area, 

 (2) an illite-chlorite-minor montmorillonite assemblage of the central area; and (3) 

 an llllte-chlorite-no montmorillonite assemblage found in the Gulf of Oman Basin. 



The montmorillonite province includes the continental shelf areas adjacent to 

 the Saurashtra Peninsula and the Gulf of Cambay, as well as nearby deep water 

 areas. Illite also is present in these sediments but In relottveiy small amounts. 



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