sedimentary
Agate
Silicon Dioxide (SiO2) - Chalcedony Variety
Hardness: 6.5-7 on the Mohs scale. Color: Brownish-yellow to translucent gray/tan with faint concentric banding. Luster: Waxy to vitreous. Crystal Structure: Microcrystalline/Cryptocrystalline (trigonal). Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Luster
- Waxy to vitreous
Identified More sedimentary →
Explore Agate in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7 on the Mohs scale. Color: Brownish-yellow to translucent gray/tan with faint concentric banding. Luster: Waxy to vitreous. Crystal Structure: Microcrystalline/Cryptocrystalline (trigonal). Cleavage: None (conchoidal fracture).
Formation & geological history
Forms primarily within cavities (geodes) of volcanic or sedimentary rocks through the silica deposition from percolating groundwater over extensive geological periods.
Uses & applications
Used extensively in lapidary arts, jewelry, tumbled stones, ornamental carvings, and historically in scientific equipment like precision balances and mortars.
Geological facts
Agates are known for their distinctive color banding caused by trace impurities like iron and manganese during layer deposition. No two natural agates are completely identical.
Field identification & locations
Identified by its waxy luster, translucency when backlit, and subtle concentric or parallel banding patterns. Commonly found along riverbeds, gravel deposits, and volcanic fields worldwide (e.g., Lake Superior region, Brazil, Madagascar).
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sedimentary Sandstone
Arenite (Sedimentary Rock)
sedimentary
Fossiliferous Concretion
Septarian Concretion containing Brachiopods/Crinoids
fossil
Shale
Shale (clastic sedimentary rock)
sedimentary
Shale
Sedimentary Shale
sedimentary
Shale and Pebble Fragment
Sedimentary Rock (Mudstone/Shale with Silica Pebble)
sedimentary