Agate
Image: <a href="//commons.wikimedia.org/wiki/User:Sailko" title="User:Sailko">Sailko</a> (CC BY-SA 3.0)
Mineral NameAgate
Chemical FormulaSiO2
Mohs Hardness6.5
Crystal Systemtrigonal
Streak ColorWhite
CleavageNone
FractureConchoidal
Specific Gravity2.6
Colorswhite, grey, brown, reddish-brown
TransparencyTranslucent
Type LocalityWorldwide
Mineral GroupSilicates
Usesjewelry, ornamental objects, collector's items
Associated Mineralsquartz, calcite, zeolites
Raritycommon
Description
This image shows a polished, translucent slice of agate, characterized by concentric bands of white, grey, brown, and reddish-brown, with a central cavity lined with tiny quartz crystals (druzy).
Geological Context
Agate typically forms in cavities within volcanic rocks, such as basalt, where silica-rich groundwater deposits successive layers of chalcedony, often filling the void completely or leaving a central druzy cavity.
