“...The chalcedony deposits (all north of Karlstetten) are related to ultrabasitic rocks (serpentinites). Old finding-areas are in "Rosenthal", near the road from Karlstetten direction Doppel... It is now a horse paddock. Recent occurrences in a sandpit east of the road from Karlstetten after Winzing... Chalcedony in beautiful red, blue, green and brown hues was found. Rockhunting only with the permission of the owner!...”

According to personal communication with Peter Huber.