Medenec (in former times “Kupferberg”) at the edge of the Czech part of the Erzgebirge was once center of a flowering mining industry on silver and copper. Today lucky agate-collectors are able to find small specimen of nicely coloured veinagates on antique ore-dumps. Two of the more important places of discovery are nowadays unfortunately completely searched out: the so-called "black Halze" at Medenec and the small finding-location at Horni Halze, in which the famous "zigzag agates" were to be found. On both places of discovery there are occuring intensively contrasting, usually red-brown and white, more rarely blue and yellow banded vein-agates. Agates from the "black Halze" are usally intergrown with minerals such as fluorite, baryte and quartz. The pattern of these vein-agates reminds in its geometrical formation of the so called “Paraiba-Agates”.
The appearance and the genesis of the so-called "zigzag agates" of Horni Halze is fascinating. One of the best interpretations of the formation of this agate type is given by Rudolf Rykart: ... at perpendicularly falling walls silica gel was separated. This flowed off slowly and at the end of the drop distance was zigzag stacked. During this procedure the gel was drained and crystallized finally. (Rykart,1989,”quartz monography”, page 373)