Scanning electron micrograph (SEM) of zeolite crystals grown in microgravity (bottom) and on Earth (top). The crystals grown in microgravity were grown in the US Microgravity Laboratory (USML-2) onboard the International Space Station (ISS). Zeolites are hydrated aluminosilicate minerals and have a micro-porous structure. Zeolite materials are being investigated for use in the storage of hydrogen fuel, for gas and vapor detection for environmental monitoring, for reducing hazardous by-products in chemical production, and for use in optical cables.