686 Subsurface Geologic Methods 



(3) roundness (or angularity) 



(4) texture of the surface 



(5) orientation 



(6) mineralogical composition 



Each of these characteristics may be defined in several ways, as for ex- 

 ample: 



Size as a width of an opening in a screen, a diameter calculated from 

 either the velocity at which a particle settles or from the measured 

 volume of the particle, or a dimension observed and estimated vis- 

 ually from microscopic examination. 



Sphericity in terms of a shape factor or the ratio of the surface of a 

 sphere equivalent in volume to that of the particle to the surface of 

 the particle. 



Roundness in terms of the ratio of the average distance to the corners 

 and edges of a particle to the radius of a circle inscribed within a 

 projection of the particle. 



Surface texture in terms of relative smoothness or in measurements 

 of pitting or striations on the surface of the particle. 

 Orientation as the direction of the principal axes of a particle re- 

 ferred to suitable coordinates in space. 



Mineralogical composition as interpretation of factors of hardness, 

 density, wettability, swelling upon hydration, shrinking upon de- 

 hydration, color and the like on some systematic basis. 



Sediments are composed of multitudes of solid particles differing in 

 size, shape, and other attributes so that each of the characteristics of a 

 particle which have been enumerated for a particular sediment can be 

 described as a frequency distribution which has as parameters a mean, a 

 standard deviation, a uniformity coefficient, probability attributes, and 

 other qualities. Indeed, the characteristics of sediments as a problem in 

 geometry are expressible in terms of at least a dozen statistical parameters, 

 depending upon which are considered to be germane to a particular argu- 

 ment. Furthermore, in addition to the unique and specific characteristics 

 of the component particles, sedimentary materials possesses aggregate or 

 mass physical properties such as, for example, porosity, permeability, 

 tensile strength, and capillary properties. The mass properties logically 

 must depend greatly upon the resultant physical properties of the com- 

 ponent particles as well as upon geo-historical phenomena, such as sort- 

 ing, packing, weight of overburden with resultant stress and strain, and 

 contact with fluids. The mass properties are determined best by experi- 

 ment, but the theory of the relationship of the properties of the component 

 particles to those of the aggregate not only is of great interest and value 

 to the student but also is a challenge to the intellect as a problem in 

 statistical geometry for which a solution ultimately should be possible. 



