Agate
Image: Hannes Grobe (CC BY-SA 2.5)
Mineral NameAgate
Chemical FormulaSiO2
Mohs Hardness6.5
Crystal Systemtrigonal
Streak ColorWhite
CleavageNone
FractureConchoidal
Specific Gravity2.6
Colorsbrown, orange, yellow, white, black
TransparencyTranslucent
Type LocalityBrazil
Mineral GroupSilicates
Usesjewelry, ornamental objects, collector's item
Associated Mineralsquartz, calcite, zeolites
Raritycommon
Description
A polished slice of agate displaying prominent concentric bands of varying shades of brown, orange, yellow, and white, with some darker, opaque layers and small vugs lined with microcrystalline quartz.
Geological Context
Agate typically forms in cavities of volcanic rocks or ancient lavas, where silica-rich fluids deposit layers of chalcedony over time, often filling amygdales or geodes.
