A 4x11cm cylinder of polycrystalline silicon, the material used to make solid state hard drives (image via ).
Continuously Cast Copper Crystal
Learned about a new process today: continuous casting. Above is a continuously cast copper crystal, 99.5% pure.
Magnesium Crystal
Ultra-Pure Silver Crystal
Ultra-pure silver crystal (more than 99.95%); via Wikipedia user Alchemist-hp.