Gypsum and anhydrite rocks consist of a single mineral: calcium sulfate. They are therefore also referred to as monomineral rocks. The main difference between gypsum and anhydrite rocks is the higher crystal water content of gypsum rock. Geologists therefore jokingly refer to anhydrite as gypsum without water. The difference is best seen in the chemical formulas of the minerals:
Gypsum: CaSO4 * 2H2O
Gypsum and anhydrite rocks usually always occur together, because anhydrite was formed from gypsum. This happened by the superposition of gypsum rock with always new sediments, so that pressure and temperature rose and the crystal water was withdrawn from the gypsum.
Conversely, gypsum can also be formed again from anhydrite over geological periods by water absorption, for example at the earth's surface. If the water penetrates deeper into the rock through fissures and crevices, gypsum can also form at greater depths.
In Thuringia, gypsum and anhydrite rock occur mainly in the southern Harz Mountains, at the Kyffhäuser, in southern Thuringia near Unterwellenborn and at the northern edge of the Thuringian Forest, i.e. also in the UNESCO Global Geopark Thuringia Inselsberg - Drei Gleichen. Gypsum sites existed and still exist, for example, between Schmerbach and Seebach, in the Drei Gleichen area at Eckhardtshög near Mühlberg or in the alabaster quarry below Wachsenburg on GeoRoute 2. Gypsum was also mined in Kittelstahl near Ruhla, in the Herzog-Ernst-Stollen near Friedrichroda (the later Mariengashöhle, GeoRoute 7) and underground in Floh-Seligenthal.
But why is gypsum and anhydrite stone so important that they were chosen as Rock of the Year 2022?
Quite simply: they are raw materials in demand, especially in the construction industry, because many of our modern building materials consist in part or entirely of gypsum or anhydrite: wallboard, gypsum fiberboard, stucco gypsum, gypsum and anhydrite screeds and cement, to name just a few. In addition, gypsum is used in the food industry, in the cosmetics and pharmaceutical industries, in medicine and in agriculture.
In Germany, approximately 10 million tons of gypsum and anhydrite stone are consumed annually. Today, a large part of the gypsum still comes from so-called flue gas desulfurization plants. The FGD gypsum is produced when the sulfur-containing power plant flue gases come into contact with a lime suspension and react chemically to form calcium sulfate. With the phase-out of coal-fired power generation by 2038, around 5 million tons of FGD gypsum will also be lost, which is why demand for natural, chemical (industrial gypsum) and secondary gypsum (recycled gypsum, processed phosphorous gypsum) will increase worldwide in the future.