Agate
Image: “Jon Zander (<a href="//commons.wikimedia.org/wiki/User:Digon3" title="User:Digon3">Digon3</a>)” (CC BY-SA 3.0)
Mineral NameAgate
Chemical FormulaSiO2
Mohs Hardness6.5
Crystal Systemtrigonal
Lustervitreous
Streak Colorwhite
Cleavagenone
Fractureconchoidal
Specific Gravity2.62
Colorswhite, grey, blue-grey, brown
Transparencytranslucent
Type LocalityWorldwide, notably Brazil, Uruguay, Mexico, and historically Idar-Oberstein, Germany
Mineral GroupSilicates
Usesjewelry, ornamental, collector, lapidary
Associated Mineralsquartz, calcite, zeolites
Raritycommon
Description
A polished, irregularly shaped slice of agate displaying concentric bands of white, light grey, blue-grey, and brownish colors, with a smooth, glossy surface.
Geological Context
Agate forms in cavities of volcanic rocks (like basalt) or ancient lavas, where silica-rich fluids deposit layers of cryptocrystalline quartz (chalcedony) over time, often filling geodes or amygdales.
