Agate is named after the Achates River in Sicily where agate was probably originally found.  It was first written about by Theophrastus (372-287 B.C.).  There are hundreds of varities of agate, each with its own unique color and pattern.  
Agate’s chief component is silicon dioxide (SiO2), and is from the quartz family.  Silicon dioxide is deposited by silica-rich water in layers, filling cavities created by gas pockets in volcanic magma below the Earth’s surface.  
Many agates are named for something they resemble.  This agate happens to look a lot like lizardskin.