55 

 Fine Quartz- Feldspar Sand 



Description 



The fine quartz - feldspar sand is a fine or very fine 

 angular sand composed primarily of quartz and plagioclase, 

 with orthoclase and heavy minerals making up only a minor 

 portion of the sediment. There is an average heavy mineral 

 content of 2.4%, and a range from 0.5 to 6.77o. The most 

 abundant heavy minerals are augite, hornblende, epidote, 

 biotite, and magnetite (Table I ). Biotite is exceptionally 

 prominent in the offshore silts and sandy silts where it is 

 the most abundant heavy mineral in the sand. 



The primary light minerals are quartz and plagioclase, 

 with quartz making up 497o of the fraction and plagioclase 42%. 

 Orthoclase averages 9%. The range of values for light minerals 

 are 49 to 607o for quartz, 30 to 49% for plagioclase, and 2 to 

 25% for orthoclase. 



Authigenic minerals are rare. Glauconite, when present, 

 is restricted in areal extent and limited to amounts less 

 than 10%. Phosphorite occurs only in traces. 



The most abundant organic constituent of these sands are 

 Foraminifera, which are present in all samples in varying 

 amounts. On the outer slopes of the bay, Foraminifera comprise 

 nearly all the calcium carbonate in the sediments. Here, the 

 percentage of calcium carbonate approaches the percentage of 

 detrital material until in some areas, the sand grades into 

 shell sand. Other organic constituents of the sands are 

 Radiolarians, diatoms, and echinoid spines, which in all cases 

 are minor in occurrence. 



