However, most banded agates from Idar-Oberstein were heated and/or dyed to create their banding effect, due to the fact that after 1834 a lot of the stone used for the marbles was translucent bluish-gray South American agate.It was long known in Idar-Oberstein that otherwise plain agates would become red when exposed to long periods of sunlight.There are many other types of semiprecious stone that can be placed in the agate category.
Specific names have been applied to agate marbles, depending on their color.
However, following this procedure they were placed into polishing drums, and depending upon the amount of time they spent in these drums the facets could be completely removed, or might remain mostly intact.
Machine ground agates, on the other hand, never have facets, though this too cannot be used as a trait to date agates.
The marble mills in this region continued operating commercially until the beginning of the twentieth century, and in fact some still operate today as tourist attractions.
The annual production is low, around 500-2000 pieces.
Carnelian agates are red to reddish brown, striped carnelian agates have alternating red and white bands, onyx agates are black, and striped onyx agates have alternating black and white bands. Dendritic agates possess "fern-like" patterns in an otherwise gray matrix, while moss agates have intertwined hair-like fibers.