An artificial calcium fluoride monocrystal that weighs 63 kilograms that is on permanent loan from SCHOTT is also one of the natural treasures on exhibition. Photo: terra mineralia/E. Mildner
Thilo Horvatitsch

Global Journey to Stone Treasures

5,000 rare minerals make ”terra mineralia” one of the largest and most significant exhibitions of its kind.

Basically all known rocks are based on minerals. Many of the crystalline ingredients tell scientists exciting stories of how the world originated billions of years ago. Presolar minerals that enter into our solar system as galactic dust can even be much older. Nevertheless, it is not only their cosmic age that is so fascinating, but also their unique variety and colorfulness. ­Natural minerals can crystallize out of aqueous solutions, hot magma melts or from the gas phase to take on various shapes and sizes of up to several meters. Mineralogy knows around 4,000 types of different compositions.
By taking place at the renovated Freudenstein Castle in Freiberg, the exhibition ”terra mineralia” is being held in a rather special environment. Photo: terra mineralia/D. Müller
For this reason, collectors have been interested in particularly rare and attractive specimens for quite some time. Dr. Erika Pohl from Switzerland, for example, has been collecting finds from all over the world for 60 years. After having put together one of the most valuable private mineral collections, she left it to the ”Bergakademie Freiberg” technical university in Germany on a permanent loan basis. The most magnificent 5,000 minerals, jewels and meteorites have been on display in the remodeled Freiberg Castle since October 23, 2008. Inside this historic 3-storey building with 3,000 square meters of space, the ”terra mineralia” exhibition embarks on a mineralogical journey around the world through Africa, Europe, America, Australia and Asia. The highlights can be found in the ”treasure chamber”. The ­antimonite displayed here ranks among the most ­valuable and beautiful exhibits. The legendary green malachite also offers a lot to talk about.
Natural minerals come in a wide variety of shapes and can be several meters in length. Mineralogy knows approximately 4,000 different types of compositions. Photo: terra mineralia/D. Müller
In addition to natural minerals, a few others are man-made. By cleverly varying parameters, such as temperature, pressure or chemical composition, synthetic crystals with special characteristics can also be created. For instance, three artificial showpieces are among the natural treasures that form the exhibition, including a 63-kilogram calcium fluoride crystal as clear as water that is on permanent loan from SCHOTT. This monocrystal features exceptionally high transmission within the deep ultraviolet spectral range and stands up to laser radiation very well. For this reason, it is often used as a preferred optical material for microlithography of nanostructures onto silicon wafers. The costly raw material and challenging high tech growing at high temperatures make calcium fluoride that is of the highest ­purity something very precious. ”The equivalent of one tablespoon of impure materials within five truck loads of crystal material would already result in too much contamination of the material for our purposes,” explains Dr. Dirk Sprenger, Director of Operations and R&D at SCHOTT LITHOTEC in Jena.

Professor Gerhard Heide, Director of the TU Bergakademie Freiberg’s earth science collections, is particularly pleased about the item on loan: ”Not only because it is worth as much as a single family home, but also because it allows us to visualize how crystals are grown industrially today for use in high-tech applications.” This, in turn, reflects yet another important ­objective of the exhibition: to show how significantly minerals actually shape our own lives.