Here's a really cool Montana Rainbow 'Iris' Agate being offered by Brad Payne, the Gem Trader, who I bought the iridescent pallasite from.
If I had money to spend I'd have this one in my collection for sure.
40.26 ct. Montana Rainbow 'Iris' Agate
Color: White / Play-of-Color Clarity: Translucent
Origin: Yellowstone River, Montana Cut: Polished Slice
Treatments: None Measurements: 50.2 x 36 x 2.3 mmTrue Rainbow 'Iris' Agate is a rather astounding gem material that is quite rare in the market. In normal reflected light, the stones look like simple Agate slices, however, once transmitted light is applied, they come alive with a full spectral display of color. The finest material comes from the Yellowstone River in eastern Montana - even when a piece is found, however, it takes an experienced polisher to bring out the colors. As the effect is caused by very thin bands within the Agate that diffract the light, the slice must be oriented in the exactly correct direction and cut to the correct thickness. Any mis-step and the stone will not show the rainbow colors.
The quality of pieces varies widely - often there is just one thin band that 'rainbows' - this one is simply magnificent. The center of the slice is fully surrounded by bands of full spectral color. Once you get the light at the right angle and intensity, you will simply be stunned by the quality and a rare piece of a phenomenal US gem material.
http://www.thegemtrader.com/Apr16IAgatePage.htm
