41 



that all organic matter is in the same state of oxidation. 

 In addition, any ferrous ions present will also be oxidized, 

 resulting in slightly higher values. 



Mineralogy 



The percentages of heavy minerals in the sand fraction are 

 determined by heavy liquid separation using acetylene tetra- 

 bromide (C2H2Br4, specific gravity 2„96 at 20OC)„ Minerals 

 having a density greater than the liquid sink while those 

 lighter than the liquid float. Thus, two different groups of 

 minerals - the "heavies" and "lights" - are separated and the 

 per cent of heavy minerals calculated. The heavy minerals are 

 then identified by standard petrographic methods. The light 

 minerals can be stained and identified using procedures out- 

 lined by Twenhofel and Tyler (1941, p. 131). Determination 

 of mineral percentages in individual samples is based upon 

 counts of approximately 200 grains. 



The sand fraction (l/l6 mm to 2 mm diameter) of each 

 sample is also usually examined with a binocular microscope 

 to establish sand types and to outline mineral associations 

 within various environments. 



Sphericity and Roundness 



Sphericity and roundness are two attributes of particle 

 shape. Roundness refers to the sharpness of the corners and 

 edges of a grain, vrfiereas sphericity is a measure of the shape 

 of a grain as related to a sphere. The sphericity and round- 

 ness of sand grains are usually determined by visual comparison 

 of the grains with charts prepared by Rittenhous (1943) and 

 Krumbein (1941). 



