H. Albert Gilg

• Dr. sc. nat. habil.
• Professor at Technical University of Munich

Summary The KINA project investigates the long-term behavior of bentonite as a barrier material in deep geological repositories for radioactive waste. By studying the natural clay transformation zones at the Kiirunavaara iron ore deposit in Kiruna, Sweden, the project provides critical insights into processes relevant to repository safety. The proj...

Disposal of high-level radioactive waste in deep geological repositories relies on both engineered and natural barriers. Bentonite clay has been universally considered as sealing materials surrounding the nuclear waste canisters. The bentonite buffer is expected to retain its sealing properties for an extended period of time in the order of hundred...

Microcracking due to thermal stresses affects the mechanical and flow properties of rocks, which is significant for thermally dynamic environments such as volcanoes and geothermal reservoirs. Compared with other crustal rocks like granite, volcanic rocks have a complex and variable response to temperature; it remains unclear how thermal microcracks...

We show EMPA analyses and water determinations of pitchstones of the Meissen volcanic complete, Saxony.

In most countries, high-level nuclear waste will be stored in deep geological repositories (DGRs). To ensure safety for up to 1 million years, DGRs are designed to maintain stable mechanical, chemical and hydrological conditions in which microbial activity is limited. Predicting the persistence, viability, and activity of a microbial community over...

The origin of volcanism in the Canary Islands has been a matter of controversy for decades. Discussions have hinged on whether the Canaries owe their origin to seafloor fractures associated with the Atlas Mountain range or to an underlying plume or hotspot of uprising hot material from the deep mantle. The debate has recently concluded, however, fo...

We present new results of a detailed mineralogical and stable isotope geochemical study of deep and significant, probably Precambrian clay alteration zones in Paleoproterozoic metavolcanic rocks in the Kiruna and Malmberget magnetite underground deposits and the Vahtanvaara iron skarn prospect in northern Sweden (Gilg et al., 2017). They are presen...

Hydrothermal alteration is considered to increase the likelihood of dome or flank collapse by compromising stability. Understanding how such alteration influences rock properties, and providing independent metrics for alteration that can be used to estimate these parameters, is therefore important to better assess volcanic hazards and mitigate risk...

Introduction: The emerald mines in the Eastern Desert of Egypt have a rich history estimated at around 2,200 years (Gilg & Grundmann, this volume). The geological history of the emeralds that were extracted from these mines is nonetheless about 600 million years old, at the end of the Precambrian era. A story that originated in the depths of the m...

Introduction: The ancient Greeks knew of a gem called “smaragdos”, which the Romans Latinize as “smaragdus”; it is the term “émeraude” that will be found in the French word later. It is believed that the Greek appellation comes from a Semitic language. The term smaragdus (or smaragdos) was obviously useful to characterize various green gems of anti...

Introduction: Although economically insignificant on an international scale, the Habachtal emerald deposit in Salzburg, Austria, is a world-renowned site. Its reputation is based on two aspects: (i) with that of Takovaya in the Ural range, it is one of only two emerald deposits of commercial importance discovered and exploited during the 19th centu...

The tensile strength of volcanic rocks is an important parameter for understanding and modelling a wide range of volcanic processes, and in the development of strategies designed to optimise energy production in volcanic geothermal reservoirs. However, despite the near-ubiquity of hydrothermal alteration at volcanic and geothermal systems, values o...

The origin of volcanism in the Canary Islands has been a matter of controversy for decades. Discussions have hinged on whether the Canaries owe their origin to seafloor fractures associated with the Atlas Mountain range or to an underlying plume or hotspot of uprising hot material from the deep mantle. The debate has recently concluded, however, fo...

Ignimbrites within calderas host intrusions with hazardous and/or economically significant hydrothermal systems. The Hvítserkur ignimbrite at Breiðuvík caldera, north-eastern Iceland, is intruded by basaltic dykes. Our data show that the ignimbrite immediately adjacent to the dyke is hard, dark-coloured, recrystallised quartz, plagioclase, and alka...

Ignimbrites within calderas host intrusions with hazardous and/or economically significant hydrothermal systems. The Hvítserkur ignimbrite at Breiðuvík caldera, north-eastern Iceland, is intruded by basaltic dykes. Our data show that the ignimbrite immediately adjacent to the dyke is hard, dark-coloured, recrystallised quartz, plagioclase, and alka...

A pectoral cross with nine emeralds and a ring containing one emerald were donated in 1786 to newly elected Abbot Dominikus Hagenauer of St Peter’s Abbey, Salzburg, Austria. Both jewels were examined by microscopy and with a portable X-ray fluorescence unit. The emeralds’ inclusion patterns and chemical properties indicate they are of Colombian ori...

The heat flux of an active volcano provides crucial information on volcanic unrest. The hydrothermal activity often responsible for volcanic unrest can be accompanied by an increase in the extent and intensity of hydrothermal alteration, which could influence the thermal properties of the volcanic edifice. Therefore, an understanding of the influen...

Volcanoes are unstable structures that deform laterally and frequently experience mass wasting events. Hydrothermal alteration is often invoked as a mechanism that contributes significantly to volcano instability. We present a study that combines laboratory experiments, geophysical data, and large‐scale numerical modeling to better understand the i...

A series of one-component aliphatic polyisocyanates has been synthesized and analyzed before and after the moisture-curing process. The resulting reactive polymers are monodisperse tetrafunctionalized reactive molecules that become aliphatic polyurea networks with enhanced tunability of mechanical, chemical, and thermal properties compared to polyu...

The collapse of a volcanic flank can be destructive and deadly. Hydrothermal alteration is common to volcanoes worldwide and is thought to promote volcano instability by decreasing rock strength. However, some laboratory studies have shown that not all alteration reduces rock strength. Our new laboratory data for altered rhyodacites from Chaos Crag...

The nature of sub-volcanic alteration is usually only observable after erosion and exhumation at old inactive volcanoes, via geochemical changes in hydrothermal fluids sampled at the surface, via relatively low-resolution geophysical methods or can be inferred from erupted products. These methods are spatially or temporally removed from the real su...

Angkor Borei, Cambodia was an important urban center related to the early first millennium C.E. polity known as Funan. Excavations in the protohistoric period Vat Komnou Cemetery site uncovered over 1300 glass and stone beads, which are important material indicators of trade. In this article, we review data from earlier studies and add new previous...

Outstanding garnet beads were found recently in an elite tumulus dated to the fourth century AD and located at the cemetery of Hagar el‐Beida in the Upper Nubian Nile Valley region. Whereas contacts of Northeast Africa with South Asia have just been proven through analysis of glass beads found in Nubia and dating to the time of intensive Indian Oce...

The physical properties and mechanical behaviour of impactites are an important parameter in fluid flow models and slope stability and landscape evolution assessments for heavily impacted planetary bodies. We first present porosity, permeability, Young's modulus, and uniaxial compressive strength measurements for three suevites from the Ries impact...

The Muschelkalk, composed of Triassic limestones, marls, dolomites, and evaporites, forms part of the Permo-Triassic cover of sedimentary rocks that directly overlies the fractured granitic reservoir used for geothermal energy exploitation in the Upper Rhine Graben. Petrophysical data for this lithostratigraphic unit are sparse, but are of value fo...

Dome-forming volcanoes are among the most hazardous volcanoes on Earth. Magmatic outgassing can be hindered if the permeability of a lava dome is reduced, promoting pore pressure augmentation and explosive behaviour. Laboratory data show that acid-sulphate alteration, common to volcanoes worldwide, can reduce the permeability on the sample lengthsc...

Hydrothermal fluids can alter the chemical and physical properties of the materials through which they pass and can therefore modify the efficiency of fluid circulation. The role of hydrothermal alteration in the development of geothermal and epithermal mineral resources, systems that require the efficient hydrothermal circulation provided by fract...

Volcanoes often host hydrothermal systems that alter the host rock. To understand the influence of alteration on mechanical behaviour of edifice-forming rock, we performed a series of triaxial deformation experiments on variably altered andesite from Mt. Ruapehu (New Zealand) under constant effective pressure. Under the imposed conditions, andesite...

Stable isotope (C–O) analysis was applied to smithsonites and cerussites from Zn(Pb) nonsulphide ores from Britain and Ireland, to determine the nature of the fluids responsible for the precipitation of secondary carbonates, and any relationship with palaeoclimatic conditions. The carbon isotope compositions of the Irish smithsonites show a major c...

An asteroid impact in southwest Germany ca. 15 Ma left a > 20 km-diameter blanket of poorly sorted clastic rock, called suevite. In the 15th century, the suevite was used to construct a Gothic church (St. George's church, Nördlingen). Visual inspection of the church highlights its strong weathering susceptibility. We investigate whether the suevite...

The mineralogical, chemical and isotopic analyses of smectites, with variable interlayer cation occupancies, from bentonite deposits in various depositional environments, reveal new insights into the boron sources and the fluids involved in bentonitization in marine and non-marine environments. Smectites from bentonites have non-exchangeable, struc...

The recently discovered giant Huoshaoyun zinc-lead deposit in the Karakorum Range, northwestern Tibet, China, consists of a major zinc-lead carbonate and a minor lead-dominant sulfide mineralization with metal reserves of zinc and lead of over 16 million tons. The zinc-lead carbonate mineralization is composed of smithsonite and cerussite, with lam...

The Sierra Mojada District comprises multiple types of near-surface mineral concentrations ranging from polymetallic sulfide zones, “nonsulfide Zn” (NSZ) deposits, and a silver-rich Pb carbonate deposit hosted by lower Cretaceous carbonate strata. Hypogene concentrations of Fe-Zn-Pb-Cu-Ag sulfides and sulfosalts are locally preserved and are associ...

Geothermal energy exploitation in the Upper Rhine Graben currently targets high-temperature anomalies in the crystalline Paleozoic basement at depths up to 5 km. However, at certain locations (e.g. Rittershoffen, France), geothermal installations are actively targeting resources at shallower depths where the Paleozoic granite transitions into the o...

Hectorite is an important industrial commodity used in cosmetics, pharmaceuticals, and drilling fluids, and is a potential source of lithium. The formation of hectorite is related to an anomalously Li-, F-and Mg-rich lacustrine environment. Various genetic models for the formation of hectorite have been proposed involving the replacement of volcani...

An Early Byzantine almandine garnet engraved with a Christian motif and dated to the late sixth to eighth century offers insight into trade practices in antiquity. The gemstone was characterized by a combination of nondestructive analytical methods including electron microprobe, portable X-ray fluorescence, Raman spectroscopy, and optical microscop...

Neapolitan Yellow Tuff (NYT) has been used in construction in Naples (Italy) since the Greeks founded the city—then called Neapolis—in the sixth century BCE. We investigate here whether this popular building stone is weaker when saturated with water, an issue important for assessments of weathering damage and monument preservation. To this end, we...

The use of Mt. Epomeo Green Tuff (MEGT) as a building stone is widespread on Ischia Island (Italy). We assess here the fire resistance of MEGT by thermally stressing samples to temperatures up to 1000 °C. Porosity and uniaxial compressive strength increase and decrease from 44% and 4.5 MPa at ambient temperature to 48% and 1.5MPa following exposure...

Schmieder et al. (2018) suggest an impact age for the Ries crater in Southern Germany that is at odds with paleomagnetic systematics and thus geologically impossible, even within its external 2-sigma error. Paleomagnetic systematics allow for only two alternative impact ages that are both tightly constrained by orbital tuning. The relative differen...

Geothermal projects in the Upper Rhine Graben aim to harness thermal anomalies that have arisen due to hydrothermal circulation within the granitic basement and the overlying Permo-Triassic sedimentary units. We present here a systematic microstructural, mineralogical, and petrophysical characterisation of the lowermost unit of this Permo-Triassic...

Phreatic eruptions are possibly the most dramatic surface expressions of hydrothermal activity, and they remain poorly understood. The near absence of precursory signals makes phreatic eruptions unpredictable with respect to both time and magnitude. The Valley of Desolation (VoD), Dominica, located close to the Boiling Lake, the second largest high...

Asteriated synthetic rubies and sapphires were produced by Wiede's Carbidwerk of Freyung, Germany, between the mid-1950s and the end of the 1970s. The rough crystals were grown slowly through a proprietary variant of the Verneuil method, developed in the mid-1950s, in the form of almost spherical to elliptical boules. After crystal growth, rutile n...

The Permian Haselgebirge Formation of the eastern Alps is among the most highly deformed evaporites worldwide. In underground salt mines, it is composed of a mélange of halite, anhydrite, and mudstone, with a subordinate amount of magmatic rocks. The only potassium mineral is polyhalite [K2Ca2Mg(SO4)4·2H2O]. Its extreme tectonic deformation provide...

The Landshut bentonites that formed from Ca- and Mg-poor rhyolitic tuffs in a fluviatile-lacustrine depositional environment of the Miocene Upper Freshwater Molasse, southern Germany, contain abundant palustrine, pedogenic and groundwater carbonates. Geochemical analyses of dolomites, calcites and smectites from bentonites of various environments b...

The Middle Miocene Upper Freshwater Molasse sediments represent the last cycle of clastic sedimentation during the evolution of the North Alpine Foreland Basin. They are characterized by small-scale lateral and temporal facies changes that make intra-basin stratigraphic correlations at regional scale difficult. This study provides new U–Pb zircon a...

Chemical and microscopic examination of the first gem-quality synthetic emeralds of facetable size proves that Prof. Richard Nacken grew two main types of emerald by flux methods in the mid-1920s. One of these two types, grown with colorless beryl seeds in molybdenum-bearing and vanadium-free fluxes, has not previously been mentioned in the literat...

Rough and faceted synthetic emeralds were produced by W. Zerfass in Idar- Oberstein, Germany, between 1963 and 1973. The synthesis process was developed in cooperation with the chemist G. H. Jaeger; experiments started in 1952 and led to samples of facetable size in the early 1960s. Microscopic examination and chemical analysis of rough and cut Zer...

The archaeological site of Arikamedu, located in Tamil Nadu State on the east coast of India, was the centre for many centuries of a significant bead-producing industry. Beads were made of both glass and stone, including garnet, but the source of the garnet rough material has not been confirmed. To probe this question, garnet beads found at Arikame...

Understanding the physicochemical conditions extant and mechanisms operative during explosive volcanism is essential for reliable forecasting and mitigation of volcanic events. Rhyolitic pumices reflect highly vesiculated magma whose bubbles can serve as a strain indicator for inferring the state of stress operative immediately prior to eruptive fr...

The salt of the late Permian Haselgebirge Fm. exposes large proportions of mudrock. The mud was trapped in a basin without a connection to the open sea. The mudrock comprises earthquake structures. An enrichment of magnesium minerals (mainly magnesite and chlorite) and “deep water” anhydrite point to a residual brine basin. Pre-saturation happened...

Mineralogical, chemical, and spectroscopic properties of chrysoberyl crystals recovered from sapphire placer deposits, related to Tertiary volcanic rocks, in the New England gem fields in New South Wales (NSW), Australia, are presented. The samples appeared yellow, yellowish brown, or brown in transmitted light, and some crystals revealed a distinc...

Dominica has one of the highest concentrations of potentially active volcanoes worldwide, flanked by abundant surficial geothermal manifestations: The Boiling Lake – Valley of Desolation area represents one of the most vigorous ones, hosting hot springs, mud pools, fumaroles, and steam vents. Intense alteration, together with predominantly phreatic...

The hydrogen and oxygen isotope compositions of bentonites and smectite-rich tuffs from the North Alpine Foreland Basin were measured for samples dated to between 9 and 21 Ma. Assuming clay mineral formation shortly after the deposition of the volcanic ash layers and at surface temperatures estimated from paleoclimatic studies, the H and O isotope...

Milky-appearing alexandrite samples from Tanzania (Lake Manyara) and India (Kerala) were examined, as were chatoyant and asteriated chrysoberyl/ alexandrite from India (Orissa), Brazil, Madagascar and Sri Lanka, and also phenomenal synthetic alexandrite from Kyocera in Japan. Sixteen oriented thin sections were studied by a combination of optical m...

Developments in emerald synthesis occurred over a period of nearly five decades (1911-1958) at a facility in Bitterfeld, Germany, operated primarily under the name IG Farben. Initial experiments involving the flux method of growth performed by H. Wild in Idar-Oberstein led to collaborations with Bitterfeld scientist O. Dreibrodt in the 1910s and 19...

The titanium content of pyrope garnet can be quantified using the intensity of a Raman band at about 830 cm⁻¹ that is normalized to the 363 cm⁻¹ band using a spectrometer-specific calibration using 10 to 15 chromian pyropes from Bohemia, Czech Republic. An accuracy of 0.025 wt% could be achieved for TiO2 contents between 0.17 and 0.67 wt% TiO2 with...

Understanding the physico-chemical conditions extant and mechanisms operative during explosive volcanism is essential for reliable forecasting and mitigation of volcanic events. Rhyolitic pumices reflect highly vesiculated magma whose bubbles can serve as a strain indicator for inferring the state of stress operative immediately prior to eruptive f...

Vigorous hydrothermal activity interspersed by sequences of phreatic and phreatomagmatic eruptions occur at Whakaari (White Island volcano), New Zealand. Here, we investigate the influence of sample type (hydrothermally altered cemented ash tuffs and unconsolidated ash/lapilli) and fragmentation mechanism (steam flashing versus gas expansion) on fr...

Dolomite and calcite in Bavarian bentonites, southern Germany, were investigated using petrography, field-emission scanning electron microscopy and stable isotope geochemistry to explore the role of authigenic carbonate formation during bentonitization. Pedogenic, palustrine and groundwater carbonates were distinguished on the basis of X-ray diffra...

A combined clay mineralogical, fluid inclusion, and K-Ar study of Upper Jurassic metasediments at the Gehn (Lower Saxony Basin, Germany) provides evidence for a transient hydrothermal event during Upper Cretaceous basin inversion centered on a prominent gravimetric anomaly. Kaolinite and smectite in Oxfordian pelitic parent rocks that cap a deltaic...

A largely overlooked form of asterism consisting of dual-color double stars is found in natural sapphire, in diffusion-treated and non-diffusion-treated synthetic rubies and sapphires, and in natural quartz. To characterize and explain this phenomenon, examples of these materials were examined. In transparent or translucent samples, an optical patt...

The natural interlayer cation composition of smectites allows a classification of economic bentonites into fully expandable and often more valuable Na bentonites and the more common Ca or Mg bentonites that require Na activation for use in specific applications. The origin of natural Na bentonites has often been attributed to formation by interacti...

Europe’s largest Fe oxide deposits are hosted in Palaeoproterozoic supracrustal rock of the Fennoscandian Shield in the northern Norrbotten province, Sweden. Significant clay alteration zones occur at the present land surface and at depth in the Kiirunavaara, Malmberget, Gruvberget, Leveäniemi and Mertainen iron oxide-apatite deposits that are host...

The recent activity at White Island volcano is primarily characterized by strong hydrothermal activity interspersed by sequences of phreatic and phreatomagmatic eruptions, down to micro-eruptions through a mud-rich crater lake. We analyzed the response of various sample types to rapid decompression caused by steam-flashing and/or gas expansion, mim...

Volcanic hydrothermal systems host a prodigious variety of physico-chemical conditions. The physico-chemical state and mechanical behaviour of rocks within is correspondingly complex and often characterised by vast heterogeneity. Here, we present uniaxial and triaxial compression experiments designed to investigate the breadth of mechanical behavio...

Stable isotope ratios can provide important evidence for estimating groundwater temperatures during the formation of clay minerals in response to chemical weathering of rocks at the landsurface. In this paper, we investigate weathering kaolins found in Buchan, NE Scotland. Stable oxygen and hydrogen isotopes for kaolins from weathered clasts in pos...

Field and microstructural data of the Pfahl shear zone in north-eastern Bavaria (Germany) reveal the intimate spatial-temporal connection between fragmentation, fluid influx and quartz crystallization. These processes and their interaction led to complex-structured quartz units: (i) a dense network of early quartz veins, (ii) two domains of fine-gr...

Fluid inclusion studies in combination with hydrogen, oxygen and sulphur isotope data provide novel insights into the genesis of giant amethyst-bearing geodes in Early Cretaceous Parana continental flood basalts at Amestita do Sul, Brazil. Monophase liquid inclusions in colourless quartz, amethyst, calcite, barite and gypsum were analysed by microt...

Bentonites in Bavaria, Southern Germany, formed in a distinct freshwater environment and often show reduced (blue, green, grey) and oxidized (yellow) facies. Soluble ions in bentonite may provide new insight into the geologic history of the clays and the composition of involved fluids assuming that water soluble ions are residues of ancient fluids....

Bentonite deposits in Bavaria (Germany) associated with authigenic dolomite and calcite formed from Mg-poor rhyolitic volcanic ash in the Mid-Miocene Upper Freshwater Molasse. The chemical composition and strontium isotope ratios of carbonates and smectites from the Mittersberg (MB), Gabelsberg (GB) and Zweikirchen (ZW) deposits were examined using...

Bentonite deposits formed from acidic rocks with high Si:Al ratios and low Mg content require intense leaching to remove silica and a source of Mg to form montmorillonite. Many rhyolite-based bentonite deposits are hosted in marine strata and seawater is usually considered as the main source of Mg in smectite. However, existing stable H-O isotope d...

The phlogopite, diopside, calcite, anhydrite and apatite pegmatites of Ampandrandava and Beraketa are examples for the many other pegmatites of similar silicocarbonatitic composition found in the Bekily and Betroka-Beraketa Precambrian belts of southern Madagascar. The two studied pegmatites and associated syenites crystallised from immiscible sili...

Mineralogy and Geochemistry of the Sedimentary Kaolin Deposits From Sinai, Egypt: Implications for Control by the Source Rocks —Mineralogical and geochemical variations among the Carboniferous and Cretaceous sedimentary kaolin deposits from Sinai provided an opportunity to examine the effect of the source area on compositions of the deposits. The C...

The Bavarian bentonite deposits near Landshut formed from distal, resedimented Mg-poor rhyolitic volcanic ash within the Upper Freshwater Molasse (UFM, Middle Miocene) of the North Alpine Foreland Basin. These important industrial clays are processed in part by acid-activation but locally contain varying amounts of carbonates that have a negative i...