Frac Sand!

The sand they use for hydraulic fracturing is very specialized.

This article is great for you because it touches on a lot of terms that we use frequently! 

"Some subsurface rock units such as organic shale contain large amounts of oil, natural gas or natural gas liquids that will not flow freely to a well. They will not flow to a well because the rock unit either lacks permeability (interconnected pore spaces) or the pore spaces in the rock are so small that these fluids can not flow through them."

This article explains that in the process of hydraulic fracturing pumps sand with bigger pore spaces into cracks to help conduct the petroleum up.

Fracking is pretty controversial for many reasons. But I like this article because it talks specifically about the materials used, especially this special sand:

"Rock units such as the St. Peter Sandstone, Jordan Sandstone, Oil Creek Sandstone and Hickory Sandstone have been potential sources of frac sand material. These rock units are composed of quartz grains that have been through multiple cycles of weathering and erosion.

That long history has removed almost all mineral grains other than quartz and produced grains with very round shapes. This is why sand dredged from rivers, excavated from terraces or removed from beaches is unlikely to produce a good product."