sedimentary
Montana Agate
Silicon Dioxide (Chalcedony with iron oxide inclusions)
AI-generated identification · may be incorrectHardness of 6.5-7 on the Mohs scale, translucent gray to white body with distinct red, orange, or black iron oxide inclusions, waxy to vitreous luster, microcrystalline structure.
Identified More sedimentary →
Explore Montana Agate in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness of 6.5-7 on the Mohs scale, translucent gray to white body with distinct red, orange, or black iron oxide inclusions, waxy to vitreous luster, microcrystalline structure.
Formation & geological history
Formed millions of years ago when silica-rich thermal waters filled cavities in basaltic lava flows, depositing microcrystalline quartz alongside iron and manganese oxides.
Uses & applications
Extensively used in lapidary arts, wire-wrapping, cabochons, and collector display pieces.
Geological facts
The distinctive red and orange spots are caused by oxidized iron (hematite or limonite) trapped within the clear chalcedony matrix during formation.
Field identification & locations
Found primarily in the alluvial gravels of the Yellowstone River and its tributaries in Montana; identified by its translucent chalcedony hosting contrasting red/black mineral inclusions.
More like this
Other sedimentary specimens
Fossil-bearing concretion, possibly containing a fossil shell or other organic inclusion
Calcareous concretion; exact fossil and host-rock composition are not identifiable from the image
fossil
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Fossiliferous Sedimentary Rock
Sedimentary limestone with invertebrate fossil imprint
fossil
Sandstone
Arenite
sedimentary
Shale
Shale (clastic sedimentary rock)
sedimentary
Shale (or Mudstone/Siltstone)
Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)
sedimentary