Our Czech agates formed in a “hot process” during volcanic episodes in the earlygeological history of our country. During the cooling of lava flows and sheets (often powerful few meters) escaping gases and bubbles stuck in magma cured. At the same empty space filled bubbles SiO2, silica solution in various modificationsenriched with other minerals such as calcite, barite, goethite, and the elementsmanganese, iron and copper.
The arrangement of mineral fillers bubbles influenced lavas heating, pressure and chemistry mentioned mixture. Thus arose the different variations ofcrystalline silica as others, geodes and agates (mossy, lace, house-shaped, etc.). Rarely filler is missing and remained free space, or a mixture of ugly, or just translucent chalcedons.
Parent rock can be volcanic, paleobazalty-melafyry, diabase, porphyry, andrhyolites, as well as sediments or weathering of the serpentine, which is usuallyrepresented as a silica opal. Smaller drawings contain agate and petrified woodcavities.
By erosion, agates get into hillsides and sediment into streams and riverbeds.Typical gravel-sand deposits in Tertiary alluvium of the Elbe, and Cidlina and Jizera, far from the source-parent rock. These deposits are called secondary.
Exact theory of agates rising does not exist. Every stone is unique in terms of layering, color range, size and especially shape that follows the space in which originated from the periphery to the center.
Written by: Kamil Kotouček, 28.11.2011