Papers by Christian Gross
Introduction and geological background Grain coarsening is a process that occurs in a wide variet... more Introduction and geological background Grain coarsening is a process that occurs in a wide variety of rock types. The application of grain growth theory to natural geologic materials has its beginnings in the theoretical foundations of the metallurgical and material sciences. Two types of grain growth can be statistically defined: 1) normal grain growth describing a uniform grain structure and 2) abnormal grain growth, where some grains grow more rapidly in size at the expense of matrix grains, thus creating a bimodal grain size distribution. This study aims to understand the grain coarsening phenomenon in metacarbonate rocks, to determine the mechanisms involved and to elucidate the role of fluids (e.g. hydrothermal alteration). Metacarbonate units exhibiting coarsely crystalline fabrics, representing abnormal grain growth, and hydrothermal alteration have been investigated from two major geologic formations of the Damara Orogen (Namibia). The study sites are located in two distinc...
Environmental Earth Sciences
Volcanic tuffs and sandstones have been used as natural building stones in the construction of mo... more Volcanic tuffs and sandstones have been used as natural building stones in the construction of monuments and buildings over the millennia of human history. Progressive weathering over time (e.g., temperature fluctuations, moisture uptake, variations in humidity, precipitation, the input of modern-day pollutants or salt crystallization) lead to damages in the internal structure of the stone. Scaling and layer-parallel flaking of rock fragments result from these types of damage-causing processes, especially when swellable clay minerals are present that lead to the generation of stresses in the rock fabric. Tuff and sandstone samples that exemplify these types of damages are investigated in this study, which were used in the construction of cultural heritage sites in Armenia, Mexico, Germany and Switzerland. Comparisons are made between these rock types considering that they show strong variations in fabric heterogeneity, grain sizes, mineralogical composition (e.g., swellable clay- an...
Environmental Earth Sciences
Many historically significant buildings and cultural heritage sites are made of volcanic tuffs. T... more Many historically significant buildings and cultural heritage sites are made of volcanic tuffs. These sites are subject to a progressive weathering and are partly in ruinous conditions. Preparing a suitable stone replacement mortar for repair work or even whole replacement stones for these rocks is of great interest. During the quarrying of tuff rocks, more than 40% of the material is rejected and cannot be further used. Utilizing this material, the production of replacement materials with optimized properties for the restoration and repair of severely damaged natural stones represents a resource-saving measure for the preservation of these buildings. In addition to the effective use of the natural stone waste, these artificial materials, in contrast to the very heterogeneous tuffs, offer a constant quality and consistent properties. A more effective exploitation can lead to a more sustainable usage of this natural resource and minimize the interference to the environment. This stud...
Environmental Earth Sciences
Many cultural heritage sites in Mexico have been built with volcanic tuff rocks from the earliest... more Many cultural heritage sites in Mexico have been built with volcanic tuff rocks from the earliest Central American civilizations to the time of the Spanish conquest and up to the present. Throughout this long period of time, the stones have been subjected to progressive weathering as evidenced by different types of damage phenomenon such as scaling, sanding, crumbling, sugaring and salt efflorescence. This study utilizes a collection of 53 tuffs from different regions in Mexico that show a diverse range of colors, rock compositions and mineralogy, and heterogeneous rock fabrics indicative of their volcanic origin. Comprehensive investigations have been done that include detailed petrographic analyses, cathodoluminescence, clay mineral analyses, and the determination of a wide range of petrophysical properties (e.g., porosity, capillary water uptake, water absorption, sorption, hydric and thermal expansion, and mechanical properties). All analyzed data combined are used for derivatio...
Zeitschrift der Deutschen Geologischen Gesellschaft, 1999
ABSTRACT The Otavi Mountain Land ore province is located in the northwestern part of the Pan-Afri... more ABSTRACT The Otavi Mountain Land ore province is located in the northwestern part of the Pan-African Damara Belt, Namibia. Polymetallic (Cu-Pb-Zn) sulfide deposits are hosted by carbonate platform successions of the Proterozoic Otavi Group within a foreland fold- and thrust-belt setting. Cathodoluminescence (CL) and geochemical data are presented for core samples from the renowned Tsumeb deposit and the active mine at Khusib Springs. The CL data reveals a wide variety of alteration phenomena providing evidence for a complex hydrothermal alteration history. The participating processes in the carbonate host rocks at both locations are solution-generated vugs and cavity formation, vein development (in part polyphase), intense brecciation, neo-mineralizations in veins, vugs and cavities, replacement and alteration, and carbonate blastesis and recrystallization of the host rock matrix. Many of the microstructures resulting from these processes indicate episodic events of penetrative fluid flow with changing compositions. Chemically both Tsumeb and Khusib Springs exhibits unique trace-element signatures related to specific fluid-related events. At Tsumeb, complex rhythmically zoned calcite cavity fillings show concentrations of PbO up to 5.9 wt. % and FeO >2 wt. % in specific growth zonations. Coexisting with these Fe-/Pb-rich calcites are pure anhedral dolomites overgrown with euhedral (rhythmically zoned) Fe-/Zn-rich dolomites, hosting ZnO compositions up to 6.5 wt %. Relatively high Pb/Zn concentrations (3.5 & 3 wt. %) were analzyed in calcite veins with cyclical growth zonations above the main ore body at Khusib Springs, suggesting a possible proximity indicator. FeO concentrations of up to 5 wt. % occur at Khusib Springs in non-luminescent, idiomorphic zones within coarse-grained sparry luminescent dolomite veins. At both localities MnO concentrations are high in both calcite and dolomite, ranging up to 2.2 wt. %, and accounting for the high luminescence and CL intensity. This data will aid in discriminating the carbonate alteration events at Tsumeb and Khusib Springs and assign those events unique trace-element signatures.
The rock-cut architecture of the Lycian culture in Turkey was created around 500 BC to 400 AC. Th... more The rock-cut architecture of the Lycian culture in Turkey was created around 500 BC to 400 AC. The remains are a testament to their building heritage. The Lycian builders created monumental sarcophagi and tomb facades with unique forms and aesthetic styles in the ancient Mediterranean world. Most of these magnificent monuments are cut into different limestone formations. They are located in an area along the southern coast of Turkey, known as Lycia after its creators.
Environmental Earth Sciences, 2018
Sandstones, clay in the form of bricks and laterite are the building materials used by the Khmer ... more Sandstones, clay in the form of bricks and laterite are the building materials used by the Khmer to construct the imposing and magnificent temples in Southeast Asia. Many of these monuments suffer from fracturing, sanding, contour scaling, crust formation and salt weathering. The affinity to weathering is closely connected to the type of material. Two sandstone types classified as feldspathic arenite and quartz arenite of Angkor as well as two arkosic sandstones from Thailand are described and investigated in this study. Important petrophysical properties determined for the different sandstones consist of hydric expansion, thermal expansion, pore radii distribution and ultrasonic velocity. Different investigations such as capillary water uptake, surface hardness, hygroscopic water sorption, and salt resistance tests were undertaken in the laboratory to characterize the various rock types. Observations and quantified damage mapping were done onsite at the Phnom Bakheng Temple. Contour scaling in the form of weathering crusts is one of the main deterioration features observable at the Angkor monuments. Comparisons are made between the building stone, the crust material from the Phnom Bakheng Temple and fresh stone material used for restoration. Significant differences in hydric and especially in thermal expansion of the crust and sandstone have been determined. The results seem to indicate that extensional processes occur, which can be considered a force for detachment (i.e., contour scaling, flaking). In an experimental trial, the hydric and thermal expansion of the weathering crust and the building stone was significantly reduced by using a weak acid for the crust and a swelling inhibitor for the original building stone.
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Papers by Christian Gross