(April 2015) Corruption in Brazil exists on all levels of society from the top echelons of political power (as seen in the MensalÃ£o Scandal and the Operation Car Wash and the Petrobras scandals) to the smallest municipalities.
Quartz sands, which are high in silica content, are used to make glass. When quartz sands are crushed they produce particles with sharp, angular edges that are sometimes used to make sandpaper for smoothing wood. Some quartz sand is found in the form of sandstone.
Other materials like plaster do not have gaps for the gas to escape. The sand used in greensand is silica, common/ordinary sand. You can use beach sand, desert sand......it's all good as long as it is clean and fine. The sand is held together with bentonite, a powdered clay.