Montana agate
Lapidary material SiO2
Also called Yellowstone agate
About it
Translucent agate with black dendrites and rusty patches, found in the gravels of the Yellowstone River in eastern Montana. Prized for scenic slabs.
- Type
- Lapidary material
- Group
- Agate (chalcedony)
- Formula
- SiO2
- Hardness (Mohs)
- 6.5–7
- Specific gravity
- 2.57–2.64
- Streak
- white
- Lustre
- waxy, vitreous (glassy)
- Crystal system
- Trigonal
- Colours
- clear, grey, white, with black dendrites and red-brown stains
- Transparency
- translucent
- Cleavage and fracture
- none; conchoidal fracture
Typical values: real specimens vary. For more, see mindat.org.