Freiberg Colloquium - Lecture: "The Secret of the Snow Head Spheres and Thundereggs".
The lecture is in connection with the special exhibition "Wunder.Welt.Achat" at terra mineralia in Freiberg.
Snow head spheres, porphyry spheres and thundereggs as well as the scientific term lithophysis are synonyms for one and the same phenomenon.
The lecture delves into the secrets of the scientific phenomenon of lithophysis, so-called high-temperature crystallisation domains. These are nodular rock formations in silica-rich volcanic rocks, which form mainly in marginal and fluid-rich parts at temperatures of 600 to 700 °C. The lecture will give an insight into the natural science of lithophysis, so-called high-temperature crystallisation domains.
Insight is given into the
the complex process of the formation of lithophyses,the internal structures of the lithophyses (sickle- and star-shaped cavities),the later filling of the internal cavities.
The lecture will focus on the miraculous world of lithophysal agates as a result of the mineralisation of the cavities through alteration and weathering, which takes place after cooling of the lava at temperatures below 200°C. On the basis of geological-mineralogical characteristics and corresponding pictures, statements are made on the following
mineralised cavity forms, agate types and crystallisation sequences,
- macro- and microstructures in the lithophysen agates.
With the classification presented, similarities but also site-specific differences can be identified for the lithophysae and their agates, because colour, shape and structure are often so characteristic that a connoisseur can already indicate the locality by sight alone. This is shown with examples of sites from all over the world.
In the special exhibition, examples of lithophysen agates from all over the world are on display, which visitors can admire as fascinating natural works of art.
Referee: Dr. Manfred Jäckel, Freiberg
The "Freiberg Colloquium" is a series of lectures by the Saxon State Office for the Environment, Agriculture and Geology; the Saxon Upper Mining Office; the Geokompetenzzentrum Freiberg e.V., the Saxon State Archives/Bergarchiv Freiberg, the TU Bergakademie Freiberg and terra mineralia.
