What is Pure Sand? SiO2...Its called Arkosic Arenite

This is a lesson I learned very early on at Field Camp...its about the difference in grade of sand. Pure sand is a collection of very mature quarts crystals...the term mature here refers to the idea that as sand is transported from one place to another the sand as a whole will loose various weaker minerals. If the sand moves around from sea to mountain and it makes it all the way to the middle of a large craton (this would be the interior of the continental USA).

Craton:

craton,  the stable interior portion of a continent characteristically composed of ancient crystalline basement rock. The term craton is used to distinguish such regions from mobile geosynclinal troughs, which are linear belts of sediment accumulations subject to subsidence (i.e., downwarping). The extensive central cratons of continents may consist of both shields and platforms. A shield is that part of a craton in which (usually) Precambrian basement rocks crop out extensively at the surface. By contrast, in a platform the basement is overlain by horizontal or subhorizontal sediments

Anyhow...the sand will then be made mostly of quarts grains that are nice and round....making this layer of rock a wonderful source rock. Source? ...a source to all sorts of things. Oil...natural gas...who knows....

A sandstone that is made mostly of quarts grains is called Arkosic Arenite. 

• classification  (in  sedimentary rock: Classification of sandstones) ...rocks whose sand grains consist of at least 95 percent quartz. If the sand grains consist of more than 25 percent feldspar (and feldspar grains are in excess of rock fragments), the rock is termed arkosic arenite or “arkose,” although such sandstones are also somewhat loosely referred to as feldspathic sandstones. In subarkosic arenite (or subarkose), feldspar sand grains likewise...
  

 Above is a chunk of quartz sandstone. 

This type of deposit is referred to as Arkosic Arenite. 

The term describes the pureness of the sandstone. 

Below is an image of sand that is mostly only Quartz grains. 

This pure sand will be moved and deposited permanently somewhere

and will form a new layer of this pure Arenitic sandstone. 

  Thanks you to Britannica Online Encyclopedia for the help with the geology terms.