Section 3.3 Chemistry and Physics of Earth Materials

Rocks are not forever. Limestone, which formed from the coral reefs of a tropical sea, is now found on alpine summits as dolomite. The lava extruded from the mouth of a volcano may eons ago have been oceanic crust that sank into the mantle during the Earth's history, and melted there. With few exceptions, all rocks take part in an ongoing cycle. Rock that is weathered at the Earth's surface collects as sediment on the ocean floor. It sinks to greater depth, finally becoming new rock, which millions of years later may be returned to the Earth's surface. We investigate what happens chemically and physically to the material during this recycling of the rock. How do melts develop? When does one phase change to another? What role do the fluids deep within the crust play? In addition to these fundamental questions related to geochemical cycles, we also investigate the properties of rocks and what they are made of. Only when we know them, can we realistically interpret the results of the geophysical measurements that the members of other departments of the GFZ collect all over the world. For these investigations, we have dozens of instruments and sensitive measuring tools at our disposal. In anvil presses we can put small samples of minerals under the pressures and temperatures that occur in the deep mantle. In the course of these high pressure experiments, we investigate, for example, the phase change as a mineral goes from one crystal form to another. In special ovens we can analyse the chemical conditions under which rocks form. We use this broad palette of experimentation and measurement tools in many different research projects. Our investigations extend from the electron spin in iron atoms deep within the Earth through the elastic properties of minerals to studies on cement and even meteorites.