Agate
Image: James St. John (CC BY 2.0)
Mineral NameAgate
Chemical FormulaSiO2
Mohs Hardness7
Lusterwaxy
Streak Colorwhite
Cleavagenone
Fractureconchoidal
Specific Gravity2.65
Colorspale yellow, cream, white, gray
Transparencytranslucent
Type LocalityWorldwide
Mineral GroupSilicates
Usesjewelry, ornamental, collector, industrial
Associated Mineralsquartz, calcite, zeolites
Raritycommon
Description
This image displays a polished cross-section of agate, revealing concentric bands of pale yellow, cream, and white, with a slightly irregular outer edge. The translucent layers show fine internal striations and a somewhat crystalline core.
Geological Context
Agate typically forms in cavities within volcanic rocks, where silica-rich solutions deposit successive layers of microcrystalline quartz (chalcedony). These layers often fill geodes, with impurities causing the distinct color banding.
