Solid materials encompass a vast range of natural and synthetic substances that maintain a fixed shape and volume at room temperature. Ten common examples include diamond (the hardest known natural carbon allotrope), iron (a dense, strong structural transition metal), quartz (a hard crystalline silicon dioxide mineral), sodium chloride (common table salt forming ionic crystals), copper (a ductile metal prized for electrical wiring), ice (frozen crystalline water), gold (a lustrous, highly malleable precious metal), graphite (a soft layered carbon allotrope), silicon (a semiconducting metalloid essential for microchips), and polyethylene (a widely manufactured synthetic polymer plastic).