Fracking is a technique where liquids and a proppant is pushed into a drilled cavity. The high pressure fractures the rock, which releases oil and natural gas. Proppants keep the rock open and allow flow of these materials out of the rock for collection and processing. A common proppant is sand, which is carefully taken and processed to ensure purity as well as correct shape and size. The Analysette 28 is a dynamic image analyzer, which takes pictures to measure particle size and shape.