Image: Anders Sandberg (CC BY 2.0)
cubiccommonSilicates (Tectosilicates, variety of Quartz)
Agate
SiO2
Agate is a cryptocrystalline variety of silica, chiefly chalcedony, characterized by its fineness of grain and often exhibiting distinct banded patterns or moss-like inclusions.
Agate Physical Properties
Mohs Hardness
7Crystal System
cubicLuster
vitreousStreak Color
whiteCleavage
noneFracture
conchoidal to unevenSpecific Gravity
2.58Colors
white, gray, blue, green, yellow, orange, red, brown, blackTransparency
translucent to opaqueType Locality
Brazil, Uruguay, Mexico, USA (Oregon, Montana), GermanyMineral Group
Silicates (Tectosilicates, variety of Quartz)Uses
jewelry, ornamental objects, industrial (e.g., mortars and pestles, precision bearings), collectorAssociated Minerals
quartz, calcite, zeolitesRarity
commonGeological Context
Agate typically forms in cavities of volcanic rocks (e.g., basalt, rhyolite) where silica-rich solutions deposit successive layers on the cavity walls, or in some sedimentary environments.
