Experimentelle Mineralogie

Research in Experimental Mineralogy

Magmatic and volcanic systems at high pressures and temperatures cannot be directly accessed for studying their physicochemical properties and associated kinetic processes. Experimental Mineralogy provides essential tools to examine these systems under controlled laboratory conditions, allowing for the determination of phase relations, the solubility and diffusion of volatile gas components, and degassing processes. These experimental findings are critical for understanding magma properties and dynamics within the Earth's interior, during explosive volcanic eruptions at the geosphere-hydrosphere-atmosphere interface, and even in the interaction of molten volcanic ash with jet engine turbine blades. 

Properties and Dynamics of Ascending Magma

The degassing of H2O-saturated silicate melt plays a critical role in influencing the dynamics of magma ascent and volcanic eruptions. Experimental investigations of H2O-rich magma under controlled decompression are key to understanding H2O fluid-silicate melt phase separation, degassing processes, and, ultimately, the interpretation of textures and volatile contents preserved in rocks and ash from high-risk volcanic systems, such as Vesuvius, Campi Flegrei, and Laacher See. These studies provide valuable insights for volcanic hazard assessment. 

Sample capsules with partially degassed hydrous Vesuvius melt. Allabar A, Nowak M (2020) EPSL 501, 192-201.
Transmitted light microscopy images of dry VAD79 starting glass and hydrous Vesuvius melt decompressed with four different decompression rates and quenched to glass at similar final pressures. The starting glass is free of vesicles and crystals. In hydrated and subsequently decompressed samples, vesicles are homogeneously dispersed and vesicle number densities are equal within error in all four samples. Vesicles in samples decompressed with ≥0.064MPa·s−1 are nearly uniformly sized and revealing similar porosities. The bright haloes visible around the vesicles out of focus are an optical effect (Becke line).The sample decompressed with 0.024MPa·s−1 has a significantly lower porosity due to diffusional loss of H2O into fringe vesicles during long decompression time before homogeneous phase separation occurred. The scale bar is valid for all images. Allabar A, Nowak M (2020) EPSL 501, 192-201.

Physicochemical Properties of Volatile-Bearing Magma

and b) show reflected light microscope images of the area mapped with ATR-FPA of decompressed and vesiculated rhyolitic samples. Intersected vesicles are dark and polished glass is light gray. c) to f) show ATR-FPA mapping results plotted with Matlabc. Each pixel represents one spectrum. The pixel size is ~1.1 × 1.1 μm. c) and d) total H2O and e) and f) molecular H2O concentrations. Allabar A, Nowak M (2020) Chemical Geology 556, 119833.

The compositional variations of gases released during active volcanic phases are not yet well understood, making it difficult to accurately model such processes. Mount Etna serves as an ideal reference system for experimental studies, as its petrology and the gas components it releases have been extensively investigated and monitored. Experimental determination of volatile partitioning between basaltic melts and complex H-O-S-Cl fluids, as a function of pressure and temperature, is essential for geochemical modeling of basaltic melt degassing. Additional key areas of focus include determining the diffusivity and diffusion mechanisms of volatiles, as well as conducting spectroscopic investigations to understand the structural incorporation of volatile components in silicate melts at high temperature and pressure.

Phase Relations in Magmatic Systems of Large Igneous Provinces and Layered Intrusions

The formation of large igneous provinces in Earth's history is often linked to global climate crises and mass extinctions, primarily due to the massive release of volatiles into the atmosphere and hydrosphere. In addition to the effects of bulk chemical composition, dissolved volatiles and oxygen fugacity play a critical role in phase relations, influencing magmatic differentiation and degassing trends. Determining the pre-eruptive conditions of magma chambers in large igneous province basalts—through comparisons of natural rock chemistry with results from volatile solubility and phase equilibria experiments under high pressure and temperature—is essential for estimating the volatile budget and degassing potential of these provinces.  

Highly fractionated, peralkaline, iron-rich mantle-derived melts from the Ilímaussaq magmatic complex (South Greenland) exhibit an unusually broad crystallization interval of over 500 °C. To trace the liquid line of descent, fractional crystallization is simulated experimentally under highly reduced conditions using multi-step experiments in graphite capsules to replicate the various stages of magmatic phase assemblages. These data are crucial for modeling the evolution of melt composition and the enrichment of rare Earth elements during the formation of complex magmatic layered intrusions.    

Back-scattered electron images of peralkaline phonolitic melt samples equilibrated experimentally at 750 °C conducted using a) high halogen and b) low halogen phonolitic starting glasses. Ae aenigmatite; Afs alkalifeldspar; Cpx clinopyroxene; Eud eudialyte; Fl fluorite; Gl glass; Nph nepheline; Sdl sodalite. Giehl´C, Marks M, Nowak M (2014) Contrib Mineral Petrol 167, 977.

Transition Metals in Silicate Melts and Crystalline Phases

Transition metals are important compatible trace elements in magmatic systems, and their mineral-melt partitioning is crucial for understanding key Earth-forming processes, such as the evolution of the mantle and crust. Spectroscopic studies have shown that the most abundant volatile, H2O, influences the coordination environment of transition elements. The formation of hydration shells around these elements significantly affects their partitioning between silicate melts, minerals, and fluids—by up to two orders of magnitude. This effect can transform transition metals from compatible to slightly incompatible elements during magmatic fractionation.

The high-pressure behavior of chromous orthosilicate Cr2[SiO4], an analogue to olivine (Mg, Fe)2[SiO4], has been studied using electronic absorption spectroscopy and X-ray diffraction in a diamond anvil cell. Experimental data indicate that, under high pressure, chromium cations form dimers with weak metal-metal bonds within the silicate structure. It is highly likely that multiple metal-metal bonds and dimerization stabilize transition metal species in silicate crystal and melt structures at high pressures and temperatures. This surprising finding provides important geochemical constraints for the fractionation of transition metals during the early evolution of the Earth.

The sequence of images shows the change of the light absorption properties von Cr2[SiO4] in VIS at two differently oriented crystal sections, parallel (001) and (010), with increasing pressure from 1 GPa to 12 GPa at room temperature. Two crystals (lower part, right upper part) within the pressure chamber are ruby crystals for pressure control. The diameter of the Diamond Anvil Cell pressure chamber is about 220 µm. Pressure medium is 4:1 methanol-ethanol. Miletich R, Nowak M, Seifert F, Angel RJ, Brandstätter G (1999) Phys Chem Mineral 26, 446-459.

Volcanic Ash Deposition in Gas Turbines and Implications for Jet Engine Safety

Jet engine test rig

The protracted grounding of commercial aircraft throughout Europe due to the Eyjafjallajökull volcanic eruption in Iceland April 2010, has alerted the public to the potential dangers of aircraft encounters with ash clouds. One of the most serious issues is the failure of jet turbines due to the deposition of molten silicate ash particles on hot turbine components. In an experimental study, we highlight the influence of volcanic ash composition, crystal/glass ratio and resulting bulk viscosity on the interaction of ash particles with hot turbine blades and vanes. A range of volcanic materials are used to simulate ash melting during transport through the combustor and deposition on a turbine blade of nickel superalloy material commonly used for the hot components in jet engines. The results show how ‘on-blade’ accumulation of molten particles can lead to efficient adhesion (wetting) and subsequent rapid accumulation of further molten material in some circumstances. In other cases particles form a cinder-like layer or entirely bounce off the blade. Any deposits will disrupt the air flow in the turbine, clog the cooling system and eventually cause the engine to stall. However, the cinder deposits can be removed in our experiments (as well as ‘in-flight’ for a real engine) by shutting off the heat source, allowing the deposit to quench and dislodge by thermal stress cracking. However, this currently recommended airplane safety procedure will not work for more basaltic melts which wet the blade surface more efficiently. Our experiments demonstrate how the nature of the incoming ash particle strongly influences the type of deposit formed, the important parameters being bulk ash composition, crystal proportion and particle size.

Improvement of High-Pressure High-Temperature Experimental Techniques

A range of high-pressure, high-temperature experimental techniques, operating at the limits of technical and material feasibility, is essential for investigating a broad spectrum of mineralogical and geological questions. These include magmatic differentiation, magma ascent and degassing, explosive volcanic eruptions, and carbon dioxide sequestration in potential host rocks at the interface of the biosphere, hydrosphere, and geosphere. Therefore, the successful development of high-pressure, high-temperature apparatuses is a prerequisite for simulating extreme conditions. This includes innovations such as the development of a sapphire anvil cell for in situ spectroscopic studies of hydrous silicate melts, improvements to pressure vessels with rapid quenching capabilities, oxygen fugacity control in pressure vessels, high-temperature gas-pressure vessel furnaces (up to 1500 °C), and a high-pressure, low-flow metering valve for controlled pressure release.

An olivine single crystal capsule technique has been successfully established for experiments with sulfur-saturated basaltic melts at temperatures above 1050 °C and high pressure. Additionally, an autoclave system has been constructed to investigate carbon isotope fractionation between CO2 gas and aqueous fluids at elevated pressures and temperatures, with the ability to sample gas and fluid phases during the experiments for carbon isotope analysis. A flow-through autoclave system was also developed and successfully operated to study CO2-fluid-rock interactions at high pressures and temperatures.

Related publications are listed here: 

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Some Research Perspectives

The fundamental goal of the "Experimental Mineralogy" research group is to gain detailed insights into the dynamic processes of the Earth’s interior that have shaped the planet’s present form and continue to influence our environment. This research provides powerful tools to investigate the composition, structure, and dynamic processes of the Earth’s interior at high temperatures and pressures. The driving motivation is to understand the interaction of fluids and volatiles (e.g., H2O, CO2, SO2/H2S, F, Cl, noble gases) with the geosphere, in order to reconstruct eruptive processes based on volatile distribution in volcanic glasses. These investigations are of both local and global significance: locally, they help assess the potential hazards for populations near active volcanoes, and globally, they contribute to understanding the climatic impacts of large igneous provinces and super-eruptions throughout Earth’s history.

A key prerequisite for modeling processes relevant to magma ascent and volcanic eruptions is a comprehensive understanding of both the kinetic and thermodynamic properties of magma at elevated pressures and temperatures. Degassing and crystallization processes significantly influence magma rheology, which in turn affects fragmentation and eruption style. The piezoactor-driven high-pressure, low-flow metering valve, coupled with a gas pressure vessel developed by our group, enables controlled continuous decompression experiments to investigate degassing and crystallization processes in a manner that closely resembles natural conditions.

Fluid-Melt-Rock Interactions: From Micron to Global Scale

Fluid-rock interactions on the micron scale are the triggers for macroscopic metamorphic processes and, at sufficiently high temperatures, lead to intense magma formation in the Earth's crust and upper mantle. Fluid-mineral-melt interactions play a crucial role in controlling magma ascent and volcanic eruptions.

Under specific pressure, temperature, and compositional conditions, thermodynamics predict the macroscopic state of an equilibrated system. However, whether on a regional or microscopic scale, fluid-melt-rock interactions are governed by dynamic nano- and micron-scale processes, including (1) solution/precipitation, (2) recrystallization, (3) surface and grain boundary diffusion, and (4) volume diffusion. To investigate the reaction kinetics of fluid-melt-rock interactions, both time and geometry must be taken into account. Chemical and isotopic heterogeneities serve as powerful tools for understanding the conditions and temporal history of these interactions, offering crucial evidence of processes and rates that impact mass transfer on a global scale. However, to interpret this data effectively, we must first understand the complex interactions among the different processes, mechanisms, and rates.

Despite substantial progress in recent decades, the interaction between fluids, melts, and minerals on a micron scale remains challenging. The key parameters that control mineral reactions, devolatilization, melt formation, fluid dissolution, and volatile degassing in dynamic systems, such as subduction zones or large igneous provinces sourced deep in the Earth’s mantle—integral parts of geochemical cycles—are still poorly understood. Therefore, linking experimentally determined fluid-mineral-melt interactions and geochemical analyses at the micron scale to large-scale geological processes presents a significant challenge.

The research perspectives outlined above highlight that Experimental Mineralogy is a critical interface between multiple research fields, including petrology, geochemistry, geophysics, applied geology, crystallography, and materials science.