Agate
Image: Hannes Grobe (CC BY-SA 2.5)
Mineral NameAgate
Chemical FormulaSiO2
Mohs Hardness7
Crystal Systemtrigonal
Lustervitreous
Streak Colorwhite
Cleavagenone
Fractureconchoidal
Specific Gravity2.65
Colorswhite, grey, brown, translucent
Transparencytranslucent
Type LocalityWorldwide, notably Brazil, Uruguay, Mexico, USA
Mineral GroupSilicates
Usesjewelry, ornamental objects, collector, industrial
Associated Mineralsquartz, calcite, zeolites
Raritycommon
Description
This image displays a sliced agate nodule, revealing concentric bands of white, grey, and brown chalcedony surrounding a central cavity lined with clear, crystalline quartz.
Geological Context
Agate forms in cavities within volcanic rocks (like basalt) or ancient lavas, where silica-rich fluids deposit successive layers of microcrystalline quartz (chalcedony) and sometimes macrocrystalline quartz, creating its characteristic banded structure.
