Montana agate has been a long time favorite of the lapidary enthusiast. Found in the alluvial gravels of the Yellowstone River in eastern Montana it has been collected and worked as a semiprecious stone for nearly a century. Noted for its clarity as well as its characteristic isolated black, and occasionally bright red dendrites, it makes excellent cabbing material. The majority of Montana agate pieces show a well-defined fortification pattern of black and brown as well as bright red/orange. There are also variations of filament and tube patterns and a small percentage display an “iris” band in which minute, regularly spaced layers act as a diffusion grating and, like a prism, break light into a rainbow of color. It is a relatively easy material to work with, being quite hard, and takes a brilliant polish.

Origin:  Montana, US

Dimensions:  2.5" x 2.25" and approximately 6.4 mm thick.  Weight = 65 g.  

Shown wet.  Not polished.  Known flaws are shown as white lines in the final picture frame.  This slab has some roughness on the back but does not interfere with the top side.