As a special souvenir of the large agate show "Celebration of Agates" in Minneapolis in 2001 I bought two types of "agate-look-alike´s" (looks like agate - but is not one), which are highly valued by lapidarists despite their clearly non-natural origin.One is the here presented "Rainbow silica" and the other was "Fordite".
"Rainbow Silica" is in the trade since 2003 and originates from Northern Mexico, from a district with factories that produce ceramics. When cutting the typical Mexican ceramic products (in particular tiles) strongly colored muds are produced which are deposited the great basins. By the pressure of the sedimentation and the stongly calcareous water the slurry is solidified and is forming brittle "stones". Before grinding this material you must soak it with tons of synthetic resin ("stabilization”) before you can work on it.
Evident is this history, if you look at the structure of the material and its inclusions. The colored, limited mostly sharp-edged particles are brecciated and sorted (caused by density-related fraction during the sinking in the liquid medium) in layers in the "Rock". Also findings of unique inclusions are made in the material, so far the most bizarre was a beer-cap.
You'll find more details in english on the website Rainbow Silica.