The study, published in Archaeological and Anthropological Sciences, examined 59 fragments selected from documented production contexts at two sites about 150 metres apart in the city’s historic pottery district. The material dated mainly from the late eleventh to the mid-twelfth centuries, spanning the Taifa, Almoravid and early Almohad periods. One workshop contained a rod kiln that had been reused as a waste dump after abandonment; the other had a clay-setting pit and production debris. The researchers regarded these contexts as more securely documented than many assemblages of decorated medieval pottery found in residential areas.

Each fragment was mounted in resin and examined by optical microscopy, while all 59 were analysed with scanning electron microscopy and energy-dispersive X-ray spectroscopy, or SEM–EDS. Twenty specimens were prepared as 30-micrometre petrographic thin sections, 14 were tested by wavelength-dispersive X-ray fluorescence, and 18 underwent X-ray diffraction. The methods were chosen to connect visible vessel traits with microscopic fabric, elemental composition and mineral phases formed during firing. Because SEM–EDS can give broader readings across heterogeneous pastes, its results were combined with petrography and XRF rather than treated as a complete chemical map.

Petrography separated the assemblage into three principal fabric groups that broadly followed function. Kitchenware belonged to Fabric F1, whose dark, fine-grained matrix contained abundant phyllite, mica schist and granite inclusions. Its cooking pots were generally low in calcium and sodium but high in silicon, with average values of about 1.5 weight per cent CaO, 0.6 per cent Na₂O and 63.2 per cent SiO₂ in the SEM–EDS dataset. Quartz-rich particles and rock fragments would have increased resistance to thermal shock. Most cooking pots were handmade, although three of the analysed examples were wheel-thrown, documenting a technological transition within the same production setting.

Water jugs formed a distinct group, Fabric F2. Their bodies were poorer in silica and richer in calcium and magnesium than the cooking pots, with a CaO/MgO ratio near 1.25. The authors interpreted this composition as evidence that at least two clays were combined: a medium-grained, non-calcareous red material resembling that used for kitchenware and a lighter clay containing dolomitic inclusions. This blended paste was also chemically similar to that used for kiln rods, suggesting that available workshop clays were adapted according to the demands of different objects. The water vessels were wheel-thrown and decorated with painted red or black designs, while their handles were sometimes made by hand.

Tableware used a finer, calcareous fabric divided into two subgroups. Both had relatively low porosity and fewer inclusions than the kitchenware, but F3-S1 contained more potassium while F3-S2 contained more sodium. Their average K₂O concentrations were about 2.6 and 0.8 per cent, respectively, while Na₂O averaged approximately 1.1 and 2.4 per cent. Neither subgroup consistently belonged to one workshop, indicating that the chemical contrast was not a simple division between the two sites. Instead, the researchers proposed that it could reflect different local clay sources, clay mixing or paste-preparation practices. Geological sampling would be required to determine whether the workshops exploited the same deposits.

The glazes showed that shared clays did not imply a single firing recipe. SEM–EDS identified 26 glazed samples, including 11 kitchenware and 15 tableware examples, along with glaze droplets from workshop equipment. Many transparent glazes contained lead and were coloured honey-yellow by iron oxide. Transparent tableware glazes ranged from 27.1 to 56.2 per cent PbO. Comparison with the ceramic bodies indicated that lead compounds were combined with quartz sand rather than applied as a simple lead coating. The tableware glazes also showed evidence of a deliberately added potassium-bearing material, possibly derived from woody plant ash, while some recipes apparently included a sodium-rich component such as salt.

Colour was produced through a limited but technically varied palette. Copper oxide generated green transparent glazes, with some samples also containing zinc, possibly indicating the reuse of brass. Brown decoration on honey-coloured tableware contained iron and manganese oxides and may have been painted onto the biscuit-fired vessel before glazing. Opaque white glaze came from cassiterite crystals formed when tin oxide was added to lead glaze. Turquoise combined copper with tin, the latter dispersing fine cassiterite particles that increased opacity. A droplet adhering to a workshop handle contained partially dissolved quartz, cassiterite and lead glaze, consistent with preparation of tin “calx,” while its wider composition included substances associated with lustre pigments. The evidence demonstrates use of lustre-related materials, but the researchers stressed that it did not conclusively prove lustreware production at either workshop.

Principal component analysis reinforced the separation of the three fabric groups: the first three components accounted for 96 per cent of the total chemical variance, with 76.9 per cent contributed by the first component alone. Mineral phases also suggested varying firing temperatures. Kitchenware containing dehydrated muscovite was probably fired below 850 degrees Celsius, while some waterware and tableware indicated temperatures of about 850 degrees or higher; analcime in one tableware subgroup pointed to vitrification above 950 degrees Celsius. Workshop equipment showed repeated exposure to heat: kiln rods contained abundant glassy phases, and one tripod stilt appeared to have been fired more than once. Overall, the evidence points to a coherent but flexible craft system, with functional choices in clay selection and multiple glazing traditions rather than highly specialised production. The study’s principal limitation is that the two selected workshops and 59 fragments cannot establish the exact source of the clays or represent every medieval pottery tradition in Almería.

Subject of Research: Archaeometric characterization of medieval pottery production, clay fabrics, glazes and colorants in Almería, al-Andalus

Article Title: Materials and technological choices in ceramic production of Medieval Almería (al-Andalus): clays, glazes and colorants

Article References: Peregrina, M. J., Molera, J., Garcia-Porras, A., Pradell, T., & Salinas, E. (2026). Materials and technological choices in ceramic production of Medieval Almería (al-Andalus): clays, glazes and colorants. Archaeological and Anthropological Sciences, 18(11), Article 219. https://doi.org/10.1007/s12520-026-02575-6

Image Credits: AI Generated

DOI: 10.1007/s12520-026-02575-6

Keywords: medieval pottery, archaeometry, Almería, al-Andalus, ceramic technology, clay fabrics, lead glazes, tin opacification, pottery workshops, X-ray diffraction, SEM–EDS, petrography

Modern geologists now understand the Lizard as an obducted ophiolite, a fragment of oceanic crust and underlying mantle rocks thrust onto the southern margin of the continent of Avalonia during the Variscan orogeny, as the Rheic Ocean closed in the early Paleozoic era. The tectonostratigraphy is remarkably complete: sheeted dykes sit atop the crustal Crousa gabbro, which is underlain by a highly sheared Moho transition zone and the Traboe cumulate complex, all resting above a mantle sequence of serpentinized lherzolite, harzburgite, and dunite peridotites. The entire sequence was thrust over a metamorphic sole, including the Landewednack amphibolite, and a complex mélange containing fragments of the Man of War Gneiss and the Mullion Island pillow lavas. Yet when the first geologists arrived in the early nineteenth century, none of this framework existed. There was no understanding of the distinction between oceanic and continental lithosphere, no theory of plate tectonics, and no coherent way to interpret the region’s complexly faulted and metamorphosed rocks.

The earliest significant survey was conducted in 1818 by Ashurst Majendie, a founding member of the Geological Society of London, who set out to map the boundaries and position of the serpentine formation around the Lizard Promontory. Working along the coast from Loe-Bar to the Helford estuary, Majendie recognized the contacts between what are now known as the Old Lizard Head Series, the Landewednack amphibolite, the serpentinized peridotite, and the Crousa gabbro, producing the first geological map of the region. Given the uniqueness of the rocks, the structural complexity of the peninsula, and the primitive analytical techniques of the day, his map is remarkably congruent with modern surveys in the positions of its major lithologic boundaries, even though the nature of the contacts and the ages of the rock bodies remained beyond his grasp.

In the summer of 1819, Adam Sedgwick, recently appointed Woodwardian Professor of geology at Cambridge, toured Cornwall in the company of the Reverend William R. Gilby, publishing his results in 1822. Sedgwick was drawn to the region because it differed so essentially from every other part of Cornwall, and he hoped to convey a correct notion of the great mineral masses that successively presented themselves along the coast. Tracing the cliffs clockwise from the Helford estuary to Mullion Cove, Sedgwick encountered the serpentine that stretches six or eight miles from coast to coast and occupies about one-third of the peninsula. He was repeatedly confounded by the poorly defined contacts between lithologies, noting that rocks at the junctions of formations were often in an advanced stage of decomposition. At Kennack Cove he struggled to describe the rapid alternation of mineral aggregates that seemed to mutually penetrate one another, and near Karak Clews he was surprised to find rocks suddenly cut off by the reappearance of serpentine, wedged between nearly perpendicular faces of the altered peridotite.

Sedgwick also left vivid descriptions of the region’s celebrated geomorphic features, including the Devil’s Frying Pan below the village of Cadgwith, which he called a magnificent natural amphitheater formed by the decomposition of serpentine, with a natural bridge of the same rock spanning the gulf where the sea had forced a passage into the chasm. Modern mapping shows that outcrops of the Lizard Peridotite, the Landewednack Amphibolite, and the Kennack Granite all occur within the circumference of that depression, details that Sedgwick suggested but could not fully resolve. He ultimately concluded that the great plateau of the Lizard was not composed of stratified rocks, and that the serpentine belonged to the class of transitional rather than primitive rocks within the classification system of his era. Notably, he and Gilby also recorded white quartz pebbles in the alluvium capping the downs north of Coverack, deposits now understood to be the Neogene Crousa gravels, though few nineteenth-century geologists considered their origin.

Subsequent workers built incrementally on these foundations. In 1822 the Reverend John Rogers read a paper to the Royal Geological Society of Cornwall, arguing that an accurate knowledge of so complex a district could only be attained by repeated examination, though his brief study of the eastern coast added relatively little beyond the four-fold division of the rocks into Devonian clay slates, amphibolite schist, gabbro, and serpentine. In 1839 Henry T. De la Beche, the first director of the Ordnance Geological Survey, published a nearly seven-hundred-page report on the geology of southwest England. Within it he recognized that the mica slates of the Lizard were of very different character from the great schistose systems of Cornwall and Devon, distinguishing the Old Lizard Head Series from the Devonian schists to the north. He also proposed that the hornblende slate had formed a basin into which the serpentine and gabbro had been poured in a state of fusion, an interpretation that was clearly incorrect but understandable given the synclinal geometry of the western coast and the difficulty of recognizing the region’s pervasive faulting.

By the 1870s, attention had shifted to the microscopic world. In 1876, professors William King and Thomas H. Rowney of Queens College Galway analyzed the Lizard serpentinite to counter the claim that serpentine was an original chemical precipitate, concluding instead that it was the product of chemical changes, which they termed methylosis, effected in a preexisting rock near the surface of the earth. King and Rowney were seasoned controversialists, having correctly identified the famous pseudofossil Eozoön canadense as interlayered calcite and serpentine of abiotic origin, and King was also celebrated for recognizing the Neanderthal as a species distinct from modern humans. Their study produced one of the most striking illustrations in nineteenth-century geology, a surrealistic composite of twenty-two distinct microscopical features, and they reviewed a series of ovoid and branching textures in the Lizard serpentine, finding them to be mineralogical rather than organic in origin.

The decisive breakthrough came from the Reverend Thomas G. Bonney of St. John’s College, Cambridge, who read the first large-scale petrographic study of the Lizard to the Geological Society of London in May 1877. Armed with the polarizing microscope, Bonney combined extensive coastal fieldwork with detailed examination of thin sections, hoping to explain phenomena with which the appliances of earlier workers could not deal. He recognized five distinct lithologies and worked out temporal relationships among them, concluding that the serpentine was originally an igneous rock formed after the metamorphism of the amphibolite, that serpentinization was complete before later intrusions, and that the dark trap dykes were the youngest rocks of the peninsula. His microscopic examinations of serpentine from fourteen locations led him to the conclusion that the Lizard serpentine was an altered olivine rock, comparing a specimen from Coverack Cove with lherzolite he collected from the type locality at Etang de Lherz in the French Pyrenees. He attributed serpentinization to the gradual decomposition of olivine by slowly infiltrated water, an interpretation broadly aligned with the methylosis concept of King and Rowney, though modern science now understands the process as a moderate to high temperature metamorphic reaction of forsterite with water and excess silica to form the serpentine mineral lizardite.

Bonney returned to the Lizard in the spring of 1882 to study the metamorphic schists, identifying a third granulitic group alongside the talco-micaceous and hornblende schists and mapping the faulted boundary between the Old Lizard Head Series and the amphibolite east of Polpeor. He observed that faults abound in the Lizard District, noting them in almost every cove and sea-chasm, echoing the observations Sedgwick had made six decades earlier. Some of his interpretations proved remarkably prescient, while others, such as his reading of current-bedding in the hornblende schists and his insistence on a conformable sedimentary sequence, were later overturned. Yet by the close of 1883, the stage had been set for the vigorous debates of the late nineteenth and early twentieth centuries, and the Lizard’s ancient ocean floor had begun, at last, to yield its secrets.

Subject of Research: History of nineteenth-century geological investigations of the Lizard ophiolite complex in Cornwall, England

Article Title: Geological investigations of the Lizard District, Cornwall, England: 1818–1883

Article References: Drummond, C. N. (2025). Geological investigations of the Lizard District, Cornwall, England: 1818–1883. History of Geo- and Space Sciences, 16(2), 65-79. https://doi.org/10.5194/hgss-16-65-2025

Image Credits: AI Generated

DOI: 10.5194/hgss-16-65-2025

Keywords: Lizard District, Cornwall, ophiolite, geology history, serpentine, Adam Sedgwick, Thomas Bonney, petrography, Variscan orogeny, oceanic crust, metamorphism, Henry De la Beche

Chondrules are the tiny, once-molten spherical grains that dominate stony meteorites known as chondrites, and they remain among the most enigmatic objects in the solar system. These millimeter-sized droplets of silicate material formed in the solar nebula some 4.56 billion years ago, predating the assembly of the planets themselves, and their textures preserve a record of the extreme, brief heating events that shaped the primordial disk. Merrill recognized early that these small spheres were not incidental curiosities but the building blocks of the most common class of meteorites, and therefore potential witnesses to the earliest moments of planetary formation. His insistence that chondrules deserved rigorous petrographic study helped transform meteoritics from a cataloguing pursuit into an experimental, process-driven science.

Drummond’s review emphasizes that Merrill’s skill lay in the emerging discipline of petrography, the microscopic analysis of rocks in thin section. By grinding meteorite samples to slices thin enough for light to pass through and examining them under polarized light, Merrill could identify the minerals, textures, and intergrowth relationships that record how a rock formed and how it was subsequently modified. He applied this technique systematically to chondritic meteorites at a time when many of his contemporaries still debated whether meteorites were volcanic ejecta, atmospheric condensates, or cosmic debris. His careful descriptions of chondrule textures, including radial and barred varieties now classified as RP, C, and BO textural types, gave later researchers a descriptive vocabulary that persists in modified form today.

The first of Merrill’s landmark papers tackled the question of chondrule origin, a problem that remains only partially resolved even now. Drawing on his petrographic observations, Merrill concluded that chondrules could not be explained by a single formation process. He argued that the diversity of textures and mineral assemblages among chondrules pointed to multiple mechanisms operating in the early solar system, an interpretation that anticipated the modern situation in which researchers have proposed no fewer than eight, and by some counts fourteen, distinct mechanisms for chondrule formation, ranging from nebular shock waves to collisions between molten planetesimals. Merrill’s pluralism, once controversial, now looks strikingly prescient in a field that has yet to converge on a single origin story.

Merrill also documented compound chondrules, pairs or clusters of spheres that appear to have fused together while still plastic, and used them to argue that some chondrules experienced more than one heating episode or collided shortly after forming. Modern researchers continue to study compound chondrules as constraints on chondrule densities in the nebula and on the timing of their formation, though the community today distinguishes carefully between compound chondrules of various textural types and the much more common porphyritic chondrules, most of which are not compound. That Merrill extracted such inferences from optical microscopy alone, without electron microprobes, isotopic analysis, or synchrotron beams, underscores how far careful observation can carry a scientist.

The second landmark paper addressed metamorphism, the alteration of rocks by heat and pressure after their initial formation. Merrill marshaled petrographic evidence that chondritic meteorites had not survived the intervening eons unchanged. Instead, he showed that their minerals and textures record a history of thermal and dynamic metamorphic alteration on their parent bodies. Chondrules in some meteorites appear blurred and recrystallized, their once-sharp boundaries softened by prolonged heating, while others show evidence of deformation and shock. Merrill’s recognition that these stones are altered rocks, not pristine nebular condensates, anticipated the modern petrologic typing scheme, in which chondrites are graded from type 3, relatively unaltered, to types 5 and 6, strongly thermally metamorphosed.

The consequences of that insight for modern planetary science are difficult to overstate. Today’s researchers read chondrites as archives of parent-body evolution: the degree of metamorphism tells them how deeply a meteorite was buried inside its parent asteroid, how large and how hot that body became, and how the decay of short-lived radionuclides drove internal heating in the solar system’s first tens of millions of years. Modern reviewers of Drummond’s paper note refinements Merrill could not have anticipated, such as the fact that essentially no static lithostatic pressure was involved in chondrite formation, so that dynamic shock rather than burial pressure explains most deformation features. Yet the basic framework, that chondrites record both primary nebular processes and secondary parent-body processing, is squarely Merrill’s.

Recognition came late but emphatically. In 1922 the National Academy of Sciences awarded Merrill the J. Lawrence Smith Medal, only its second presentation, for outstanding accomplishments in the study of meteorites, citing in particular the pair of papers on chondrule origin and chondrite metamorphism. By then Merrill had risen to head curator of geology at the National Museum, and his students and successors had carried his methods into a growing American research enterprise. Even his name became embedded in the science itself: the phosphate mineral merrillite, a trace but ubiquitous accessory phase in chondrules, commemorates his contributions every time a researcher logs its presence in a thin section.

Drummond’s historical analysis also traces how Merrill’s hypotheses were received and refined by subsequent generations. The peer discussion accompanying the preprint, including detailed commentary from meteoriticist Alan E. Rubin, situates Merrill’s observations within modern classifications, noting for example that the plagioclase feldspar Merrill found scarce in his samples is essentially absent in petrologic type 3 chondrites and only grows to visible sizes in types 5 and 6, exactly as the metamorphism framework predicts. Reviewers likewise note that while nearly four dozen mineral phases have been identified in chondrules, more than 98 percent of chondrules in ordinary and carbonaceous chondrites are dominated by olivine, low-calcium pyroxene, and silico-feldspathic glass, with minor metal, sulfide, and accessory phases, a simplification that makes Merrill’s optical-era descriptions remarkably durable.

What emerges from Drummond’s review is a portrait of a scientist whose patience with small stones yielded insights of cosmic scale. At a time when the solar system’s origin was a matter of speculation, Merrill treated meteorites as data, read their microtextures as records of process, and concluded that both the formation of chondrules and the alteration of chondrites were complex, multi-stage histories rather than single events. Every laboratory that today heats dust aggregates to simulate chondrule formation, every mission that returns material from a primitive asteroid, and every petrologic type assigned to a newly fallen stone operates within the framework he helped construct. The tiny spheres he studied under the microscope a century ago still carry the oldest story ever told, and George Perkins Merrill taught science how to read them.

Subject of Research: Historical analysis of George Perkins Merrill's petrographic research on chondrules and metamorphism in chondritic meteorites

Article Title: George Perkins Merrill's Analyses of Chondrules and Chondritic Meteorites

Article References: Drummond, C. N. (2026). George Perkins Merrill's Analyses of Chondrules and Chondritic Meteorites. https://doi.org/10.5194/hgss-2026-9

Image Credits: AI Generated

DOI: 10.5194/hgss-2026-9

Keywords: George Perkins Merrill, chondrules, chondritic meteorites, meteoritics, Smithsonian, metamorphism, solar system origin, petrography, J. Lawrence Smith Medal, history of science, chondrites, Carl N. Drummond

The setting alone makes the work compelling. Bangladesh sits atop the Bengal Basin, one of the world’s great sedimentary repositories, where strata eroded from the rising Himalaya and carried by the Ganges, Brahmaputra and Meghna rivers have buried the ancient crust under hundreds to thousands of metres of Late Permian to Quaternary sediment. In the northwest, however, the Precambrian basement rises unusually close to the surface. The shallowest known occurrence lies at just 128 metres depth at Maddhapara, where diorite-tonalite-granodiorite rocks have been dated at 1.64 to 1.73 billion years using U-Pb SHRIMP analysis of zircon. That age places the Dinajpur Block firmly within the Paleoproterozoic, an era when the planet’s landmasses were assembling into the supercontinent Columbia, also known as Nuna.

Until now, drill hole GDH-62 had never been examined petrographically. The team collected nine core samples from the Geological Survey of Bangladesh repository and prepared twenty-seven thin sections, two or three per sample to capture mineralogical variation along and across the core axis. Under a standard polarizing microscope, they identified minerals and counted them along twenty-five to thirty-five grid-based traverses per section, estimating modal compositions visually with an uncertainty of about plus or minus five percent for major minerals. The approach is deliberately classical, but it is exactly the kind of careful, quantitative petrography that turns a stack of grey core boxes into a readable geological history.

The results split cleanly into two rock families. The felsic rocks, which occupy about 20.2 metres of the core or roughly 73 percent of the studied interval, are granodiorite: massive, grey to greenish grey, leucocratic to mesocratic, and fine to medium grained. Their modal composition ranges from 33.4 to 49.2 percent plagioclase, 11.8 to 27.0 percent quartz, 6.6 to 27.2 percent biotite and 6.7 to 11.7 percent K-feldspar, with secondary chlorite and epidote and accessory muscovite, zircon, hematite and opaque minerals. Plotted on the standard Quartz-Alkali Feldspar-Plagioclase discrimination diagram, every felsic sample falls within or adjacent to the granodiorite field, some near the granodiorite-tonalite boundary. The textures are hypidiomorphic and inequigranular, with fine- to medium-grained interlocking fabrics that speak of slow crystallization in a deep plutonic environment.

The microscopic detail is where the rocks begin to tell their deformation story. Quartz grains show wavy, undulose extinction, a classic signature of strain accumulated in the crystal lattice, and locally the quartz has recrystallized into finer equant aggregates. Biotite occurs as blade-like, euhedral to subhedral crystals with light brown to yellowish brown pleochroism, and many grains are twisted, bent and partially foliated. Aligned biotite and chlorite along recrystallized quartz grain boundaries define a weak foliation whose intensity, notably, decreases with depth in the section, hinting at a gradient in deformation intensity that the authors caution cannot be quantified from petrology alone. K-feldspar displays textbook Carlsbad twinning and hosts inclusions of acicular muscovite, biotite and rare epidote, the latter possibly pointing to hydrothermal alteration. Plagioclase shows weak to moderate sericitization, and much of the biotite is altered to chlorite, evidence that fluids, possibly of hydrothermal origin, percolated through these rocks long after they crystallized.

Cutting through the granodiorite near the base of the hole is the study’s most eye-catching discovery: an appinite dyke, massive, greenish grey to very dark green, and dominated by hornblende at 67 to 73 percent of its mode, accompanied by biotite, plagioclase, chlorite, hematite and accessory opaque minerals, with calcite forming micro-veins and veinlets. Appinites are an unusual and petrogenetically significant class of rock, typically hornblende-rich mafic intrusions associated with hydrous, mantle-derived magmas in convergent settings. In thin section the appinite shows hypidiomorphic, inequigranular and locally poikilitic textures, with hornblende enclosing plagioclase crystals. Hornblende exhibits the characteristic amphibole cleavage angles of 56 and 124 degrees with extinction angles between 12 and 34 degrees, while reddish brown biotite suggests a titanium-rich composition that the authors flag as potentially significant for petrogenesis. A tentative identification of orthopyroxene, based on pleochroism and parallel extinction, remains unconfirmed without optical or chemical constraint on its 2V angle.

The contact between the dyke and its host is sharp and non-gradational, with no chilled margin, and the authors interpret it as evidence that the appinite was emplaced after the felsic host had consolidated, most likely as a hypabyssal dyke within the main acid to intermediate association. From granodiorite to appinite, quartz and plagioclase decrease while biotite increases, tracking the shift from felsic to mafic chemistry. What petrography cannot constrain, the researchers emphasize, is the emplacement depth, a limitation they state plainly rather than paper over. That honesty matters in a field where over-interpretation of thin-section evidence is a chronic hazard.

Perhaps the most technically rich part of the study is its analysis of vein microstructures, which function as a kind of strain gauge for events long after the magmas cooled. In the granodiorite, lensoidal quartz veins with smooth vein-wall interfaces and lensoid wall-rock fragments point to a fracture-controlled vein system formed by syntaxial growth, in which crystals grow from both walls toward the vein centre. The small angle between the growth phase and the crack wall suggests a low growth rate, and the absence of fluid inclusions indicates that the vein crystals were deformed under non-hydrostatic stress during or after formation. In the appinite, by contrast, monomineralic calcite veins show slightly curved growth and selvages at their margins, hallmarks of antitaxial growth in which crystals expand outward from the vein centre, recording progressive, stress-related deformation over time. Minor calcite veins oriented obliquely and sub-parallel to the major vein hint at changing stress directions and possible fracture reactivation across the life of the intrusive complex.

The comparison the authors draw with the West African Craton gives the work its global resonance. Paleoproterozoic granitoids of the Bas Draa inlier in Morocco’s Anti-Atlas, dated around 2.1 billion years, share calc-alkaline, subduction-related characteristics with the Dinajpur Block, and both regions feature sodic TTG-style suites derived from partial melting of hydrated mafic sources. Mafic and appinitic dykes in GDH-62 resemble the lamprophyric dyke swarms of the West African Craton, though the Bangladeshi examples point more strongly to metasomatic and mantle-wedge influences than to plume-related processes. The similarities support the interpretation of GDH-62 as a fragment of Paleoproterozoic arc crust, a piece of a convergent-to-collisional margin that helped stitch together Columbia. For a country whose geology is usually described in terms of deltas, floods and gas fields, the message is striking: beneath the youngest sediments lies a two-billion-year-old arc, complete with dykes, veins and deformation histories, waiting in core boxes for anyone patient enough to grind the thin sections.

Subject of Research: Petrographic characterization of Precambrian crystalline basement rocks in drill hole GDH-62, Dighipara, northwest Bangladesh

Article Title: Petrographic characterization of the crystalline basement in Dighipara, Northwest Bangladesh

Article References: Zahan, H., Ameen, S. M. M., Hossain, M. S., & Hossain, M. S. (2026). Petrographic characterization of the crystalline basement in Dighipara, Northwest Bangladesh. Discover Geoscience, 4(1), Article 332. https://doi.org/10.1007/s44288-026-00703-2

Image Credits: AI Generated

DOI: 10.1007/s44288-026-00703-2

Keywords: petrography, crystalline basement, granodiorite, appinite, Bangladesh, Dinajpur Block, Bengal Basin, Precambrian, vein microstructures, Columbia supercontinent, drill core, hornblende

Thuburbo Majus lies roughly sixty kilometers southwest of Tunis, near the modern town of El Fahs, in a fertile agricultural zone that helped the city flourish from the first through the seventh centuries CE. Granted civic status probably under Augustus and later elevated to the rank of honorary colony under Commodus in 188 CE, the city accumulated temples, a forum, a Capitolium and public baths. The Winter Baths, covering approximately 1,600 square meters in the urban core, grew through an asymmetrical layout born of repeated additions and renovations. An inscription studied in earlier scholarship allowed archaeologists to attribute the original construction to the first half of the third century CE, with major restoration phases in the late fourth to early fifth centuries and again in the early sixth century, before the building’s eventual abandonment.

The research team, led by Aida Zaddem and Karima Zoghlami with colleagues including Rafael Fort of the Institute of Geosciences in Madrid, sampled nine distinct stone lithotypes and thirty-two mortar specimens from walls across the complex. Petrographic thin sections, stained to distinguish calcite from dolomite, revealed the full petrographic identity of each rock: a nummulite-rich Oligocene packstone, travertine, ferriferous recrystallized micrite, a dense Jurassic limestone marketed even today as Aziza-type marble, a porous bioclastic calcarenite, speleothem calcite, an Eocene biomicrite, a Jurassic pelsparite and a glauconitic grainstone. Each of these was matched to a specific architectural role, and the match turned out to be strikingly deliberate.

The analysis exposed a procurement strategy of remarkable economy and precision. Nummulitic limestone and travertine, quarried within a radius of less than twenty kilometers, formed the monumental framework, minimizing transport costs while providing the mechanical strength the main structures required. The heating system told an even sharper story. The vault of the main furnace, the praefurnium, was built exclusively of fired bricks bonded with cocciopesto mortar, a technical imperative given that flames there could reach between 800 and 1,000 degrees Celsius, hot enough to decarbonate and disintegrate any carbonate stone. Yet the support pillars and the cheeks of the flue channels, made of glauconitic limestone and ferriferous micrite, remained intact, demonstrating that builders understood empirically that temperatures at those positions stayed below the limestone destruction threshold of roughly 600 to 800 degrees.

Specialization extended to the prestigious elements. Highly porous calcarenite, with porosity reaching 25 to 27 percent, was reserved for arches and voussoirs where lightness mattered, while marbles were chosen for columns, where hardness and visual prestige dominated. The mortars, meanwhile, fell into two great families: lime-based and gypsum-based. The lime mortars split into three subgroups that map directly onto Roman hydraulic science. The first type, moderately hydraulic, mixed a lime binder with siliceous and carbonate aggregates likely drawn from the sands of the nearby Oued Miliane and Oued Medjerda rivers; their hydraulicity came from clay impurities in marly limestone calcined into the binder itself, forming calcium silicate and aluminate hydrates without any added ceramics.

The second type was entirely different in purpose: non-hydraulic air-lime coatings built in multiple layers, their aggregates composed of crushed marble and vein calcite, with grain size progressively decreasing from the wall inward toward the finished surface. These white to beige plasters carried the highest calcium oxide contents of the entire assemblage, averaging around 57 percent, and their chemistry shows almost no silica, alumina or iron, confirming a purely aerial binder. Fascinatingly, one intermediate layer in some samples shows a faint reddish hue and weak hydraulic character, hinting that builders may have sprinkled finely ground ceramic powder, an artificial pozzolana, into that single stratum to fine-tune its properties. This kind of marble-dust coating echoes the plaster recipes that Vitruvius described for polished wall finishes.

The third lime type is the showpiece: highly hydraulic cocciopesto, loaded with ceramic fragments up to a centimeter across, used to waterproof the frigidarium pool and a decantation basin. Thermal analysis sealed the classification. The ratio of carbon dioxide to water lost during heating, a standard proxy for hydraulicity, dropped below 5 percent for these mortars, the signature of strongly hydraulic systems in which pozzolanic reactions between lime and fired clay generate abundant calcium silicate hydrates. Trace elements told the same story from another angle: cocciopesto samples carried the highest concentrations of niobium, rubidium, zirconium, zinc, chromium and vanadium, the geochemical fingerprint of silicate-rich ceramic aggregate. A fourth family of gypsum-based mortars, dominated by sulfate phases with sulfur trioxide averaging over 63 percent, came from the abandonment phase, when builders opportunistically exploited abundant local Triassic gypsum deposits even in structural roles that gypsum was traditionally never asked to play.

Perhaps the most consequential findings are chronological. Mortar fingerprinting forced a re-evaluation of the building’s accepted construction sequence. A joint mortar from the latrines, previously assigned to the first renovation phase of the late fourth century, proved compositionally indistinguishable from the original third-century mortars, raising the possibility that the latrines were part of the initial design and only internally modified later. A coating from the corridor wall, attributed to the original phase on architectural grounds, instead matches the crushed-marble plasters of the late-fourth-century renovation. Most strikingly, the bottom of the decantation basin, built with original-phase cocciopesto, contrasts with its upper walls of gypsum-bonded rubble, suggesting the basin’s base belongs to the first construction campaign while its upper portion was added during abandonment, a functional repurposing of the water system. The authors caution that these reinterpretations remain preliminary until confirmed by absolute dating methods such as optically stimulated luminescence or isotopic analysis.

The study also carries a warning for conservation. Soluble salts, including halite, syngenite and secondary gypsum, pervade the mortars. The gypsum largely results from the dissolution and recrystallization of older gypsum binders migrating through the masonry; the halite, at an inland site, most likely rose capillary-ward from saline groundwater or came from unwashed, evaporite-rich local sands; and syngenite forms when gypsum reacts with potassium from atmospheric deposition or fertilizers. These salts crystallize and swell with humidity, and their behavior directly explains the poor state of preservation visible across the complex today. Any modern repair mortar that ignored this chemistry would accelerate rather than arrest the decay.

In the end, the Winter Baths emerge as a case study in how Roman builders married imperial engineering knowledge to local geology, balancing logistics against performance with a precision that thermal modeling has only now made legible. By treating mortars not merely as glue but as chronological and technological documents, the research provides both a corrected timeline for the monument’s evolution and a rigorous template for designing compatible restoration materials, one based on the very recipes Roman craftsmen mixed nearly eighteen centuries ago. For a site whose excavated area still covers only a fraction of its ancient footprint, the stones and mortars of Thuburbo Majus are proving to be its most eloquent historians.

Subject of Research: Archaeometric characterization of Roman building stones and mortars from the Winter Baths of Thuburbo Majus, Tunisia

Article Title: Multi-analytical characterization of construction materials from the ‘Winter Baths’ of Thuburbo Majus (Tunisia): Implications for architectural chronology and conservation

Article References: Zaddem, A., Zoghlami, K., Fort, R., Romdhane, H. B., Coralini, A., & Gasmi, M. (2026). Multi-analytical characterization of construction materials from the ‘Winter Baths’ of Thuburbo Majus (Tunisia): Implications for architectural chronology and conservation. Archaeological and Anthropological Sciences, 18(10), Article 205. https://doi.org/10.1007/s12520-026-02563-w

Image Credits: AI Generated

DOI: 10.1007/s12520-026-02563-w

Keywords: Thuburbo Majus, Roman baths, archaeometry, mortars, hydraulic lime, cocciopesto, petrography, X-ray diffraction, Tunisia, conservation, building chronology, gypsum mortar

That question has now been answered with laboratory evidence rather than stylistic argument. In a study published in American Antiquity, researchers at the Florida Museum of Natural History combined chemical fingerprinting with microscopic analysis of pottery from Tampa Bay and concluded that the vessels were made locally by migrants from the Florida Panhandle, the center of gravity of Mississippian culture. These artisans apparently carried specialized knowledge of clay processing and vessel construction hundreds of miles south, then used that expertise to establish a niche for themselves within the region’s existing Safety Harbor communities. The findings resolve a debate that has simmered since the sherds were first shelved in museum collections a century ago.

The cultural backdrop explains why the pottery was so puzzling. Around 1000 A.D., a new way of life took root in the Mississippi River Valley and radiated outward across much of the Midwest and eastern United States. In the heartland, Indigenous communities organized into regional hierarchies, with large chiefdoms concentrating political power over surrounding villages. They planted extensive fields of maize and quarried earth to build flat-topped mounds crowned with temples and elite residences. Tampa Bay, by contrast, sat on the southern edge of this world. The regional culture there, known as Safety Harbor, shared some Mississippian traits: communities aggregated into small chiefdoms, the largest centered on the Tocobaga, with the Mocoso, Pohoy and Uzita chiefdoms nearby, and they too built platform mounds. But no local group amassed the political scale of the northern centers, and the coastal communities never adopted maize agriculture, sustaining themselves instead on fishing and marine resources.

Given these mixed signals, archaeologists never fully understood how closely the coastal chiefdoms were tied to the Mississippian heartland, and the presence of Mississippian-style decorated pottery only deepened the uncertainty. Surface designs alone could not settle the matter, because motifs can be copied. What was needed was a way to look beneath the decoration, into the invisible decisions a potter makes before a vessel is ever fired. Trevor Duke, who began the research as a doctoral student at the University of Florida, and his colleagues assembled a sample of 58 pottery sherds from Tampa Bay, including both plain wares used for everyday cooking and serving and decorated vessels likely reserved for special occasions.

The first test targeted the clay itself. Using neutron activation analysis, the team measured the chemical composition of the sherds and compared it with that of raw clay sources around the region. The profiles matched, showing that every vessel in the sample, decorated or plain, had been made on-site from local clay. That result eliminated the trade hypothesis: the pots had not been manufactured in the Mississippian heartland and carried south. But chemistry could not yet rule out imitation, because a local potter copying northern designs would also use local clay. The decisive evidence had to come from the recipe hidden inside the paste.

To recover it, the researchers turned to petrography, a technique in which a thin slice of a pottery sherd is polished down to roughly half the width of a human hair. Light from a polarizing microscope passes through the section, revealing the voids, cracks and mineral grains that record how the clay was processed. The minerals can be identified by their color and shape under magnification, and from that, researchers can determine what was mixed into the clay. It is, in effect, a fingerprint of the people who made the vessel, preserving choices that no surface decoration can disguise.

Under the microscope, the Tampa Bay pottery revealed its secret. Several of the decorated fragments were tempered with grog, crushed pieces of old pottery mixed into fresh clay, a hallmark of some Mississippian pottery that improves a vessel’s ability to withstand the high temperatures of firing and cooking. Grog tempering appeared in none of the plain samples from Tampa Bay, but in the Tallahassee Hills, home to the nearest massive Mississippian mound center some 200 miles to the north, it is the standard tempering technique for all vessels. The connection ran deeper still: within the grog, the scientists identified mica, a shiny silicate mineral common to the Panhandle but not typically found in peninsular Florida. The host clay was local, but the particles mixed into it had come from the Mississippian heartland, apparently carried south by the potters themselves.

The contrast between the two vessel classes was stark. While 80 percent of the decorated pottery contained grog, not a single plain sherd did; most plain vessels were tempered with chunks of dry clay or sand, methods used in the region for the previous 3,000 years. The decorated pots were also shaped by coiling, the Mississippian technique, rather than molding, and were made with more consistent paste recipes, suggesting potters with advanced knowledge of clay processing. The plain wares, by contrast, were molded, a simple practice that could be quickly learned by novices as the region’s population grew. The most likely reconstruction is that migrant potters traveled from northern Florida carrying bags of their old decorated vessels, then crushed and ground that homeland pottery into the fresh clay of their new home. Every grog-tempered vessel contained multi-generational grog, fragments embedded within larger fragments like Russian nesting dolls, traceable through several generations of pots, and always drawn from the same lineage of decorated vessels. The migrants were quite literally incorporating pieces of their homeland into everything they made.

That expertise appears to have been the migrants’ ticket into an unfamiliar society. Their skill and their connection to Mississippian tradition would have set them apart, transforming commonplace homeland practices into valued services. Yet the knowledge stayed confined. The distinction between decorated and plain pottery persisted for centuries, and local residents never adopted the new techniques, whether because access was restricted or because the skills were simply too tightly held. The tempering, coiling and paste consistency are not clearly visible in a finished pot, so they cannot be easily mimicked without intimate access to the makers. The decorated vessels were also made from higher-quality clays than the plain wares, indicating the migrant artisans were granted access to a limited resource. As one of the researchers noted, secrets of this kind must be broadcast in part, so that people know a secret exists, and the circulating high-quality pots did exactly that, advertising a craft whose inner workings remained out of reach.

The study also offers a broader lesson in how migration reshapes material culture. Specialized knowledge passes directly from mentor to learner, and by tying homeland pottery into a chain of crushed and reused fragments across generations, the migrant potters may have been carrying their ancestors’ vessels into each new pot and the next generation. In Tampa Bay, a community of artisans found a way to matter in a new place, and the evidence of their arrival was hiding in plain sight for a century, waiting for the right instruments to read it.

Subject of Research: Compositional analysis of Mississippian-style pottery revealing migrant potters in pre-Columbian Tampa Bay, Florida

Article Title: Archaeologists uncover centuries-old mystery of Tampa Bay’s secret community of migrant potters

Article References: Archaeologists uncover centuries-old mystery of Tampa Bay’s secret community of migrant potters. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Mississippian culture, Tampa Bay, Safety Harbor, pottery analysis, neutron activation analysis, petrography, grog tempering, migration, Florida archaeology, American Antiquity, Tocobaga, Florida Museum of Natural History

Utrecht occupies a special place in medieval Dutch ceramic history. The earliest evidence for pottery production there dates to the late 12th century CE, and by the 14th century the town had joined Haarlem, Leiden and Breda as a major manufacturing centre supplying both local markets and wider regional trade. Its products have been recovered as far afield as Alkmaar, Haarlem, Dordrecht and Amsterdam. The workshops themselves clustered in the suburbs of Bemuurde Weerd and Tolsteeg, north and south of the town walls, and along the banks of the Vecht river, where excavations have uncovered nine vertical updraft kilns with brick or clay floors, round or oval in plan and measuring up to five metres long.

The excavated waste heaps tell a story of technological transition. The first production phase at Zeedijk, dated 1150 to 1175 CE, yielded almost exclusively grey, round-based jars. After an apparent hiatus of roughly a century, the second phase, from 1275 to 1350 CE, saw a wider repertoire including lead-glazed reddish tripod forms, jugs, bowls and pans, though grey jars remained dominant. By the third phase, represented by the Oosterkade workshop (1350 to 1400 CE) and riverside workshops such as Anthoniedijk, Hogelanden and Lauwerecht (1375 to 1425 CE), lead-glazed redware had become far more prominent, and unglazed and lead-glazed floor tiles were also being produced.

To characterise the raw materials and firing technology, the team subjected the 59 samples, plus one clay sample from a waste pit at Bemuurde Weerd, to a battery of techniques: polarised light optical microscopy, wavelength-dispersive X-ray fluorescence spectrometry, X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectrometry. Thin-section petrography revealed two main fabric groups, a Coarse Group with large, moderately to poorly sorted quartz inclusions and a Fine Group with smaller, better-sorted inclusions. The size, rounded shape and bimodal distribution of the coarse quartz grains suggest they were deliberately added as temper, most likely derived from fluvial deposits, consistent with the Holocene river clays of the region.

The chemical data, measured on 26 major, minor and trace elements at the Fitch Laboratory of the British School at Athens, showed a strongly homogeneous, silico-aluminous dataset pointing to local clay sources. Principal component analysis identified three compositional groups, with a large, homogeneous group A accounting for more than 70 percent of the samples. All the Utrecht products were made from calcium-poor, iron-rich clay, with calcium contents below 2.5 percent, and the chemical similarity between the fired clay sample and the pottery, despite differences in calcium, may itself be evidence of quartz tempering. X-ray diffraction confirmed the mineral assemblage of quartz, illite-muscovite, K-feldspar and plagioclase, with redware bodies generally containing more hematite than greyware.

Firing temperatures emerged as consistently low. Most of the ceramics, 44 of them, were fired below 800 degrees Celsius, while a handful containing the high-temperature minerals gehlenite, diopside and mullite may have reached roughly 850 to 900 degrees or slightly above. The co-occurrence of surviving calcite and dolomite with these high-temperature phases implies short soaking times in the kiln. The glazes told their own story: single-layered, transparent coatings up to about 250 micrometres thick, of very high to high-lead type, with lead oxide contents between roughly 51 and 69 weight percent. Comparisons of corrected glaze and body compositions indicate that potters mixed lead oxide with silica before application, and that the yellowish-brown to greenish colour came from iron in the glaze over the reddish ceramic body.

The most novel element of the study was the application of small-angle neutron scattering, or SANS, to the question of how the vessels were formed. Measured non-destructively at the YS-SANS instrument of the Budapest Neutron Centre, 38 jar samples yielded data on the orientation and alignment of nanoscale domains in the ceramic fabric, which record the forces applied during forming. Thirty-two samples showed high isotropy values, indicating disorganised internal structures characteristic of percussion-building techniques such as pinching, moulding or tamper-and-concave-anvil forming. Combined with the wheel-made traces on rims and necks, this points to a two-stage strategy the authors call percussion-wheeling: the body formed by percussion, then the neck and rim refined on a rotational device.

Only six samples showed the low isotropy and significant tilting angles diagnostic of other techniques. One redware jar from the second phase at Zeedijk proved to be coil-built and wheel-shaped, while five jars, from both Zeedijk and Oudenoord, were genuinely wheel-thrown, three with clockwise and two with anticlockwise wheel rotation. Notably, all the wheel-thrown examples date to the second production phase after about 1275 CE, confirming a previously observed typo-technological shift from grey hand-formed jars to reddish tripod forms. Contrary to common expectations, the potters did not favour fine fabrics for wheel-throwing; nearly all the wheel-thrown jars were made from the coarse fabric. The persistence of percussion-wheeling across the 100-year hiatus between the first and second phases suggests a conservative, culturally embedded technological tradition, one perhaps also suited to producing the round-based jar shapes that were difficult to throw on a wheel.

The study also cautions against reading forming techniques from surface features alone. Interior depressions often interpreted as fingertip impressions from moulding appeared on wheel-thrown vessels too, and may instead reflect hands supporting the vessel wall during brushing, while interior ridges below the neck, sometimes taken as evidence of added coils, also occurred on wheel-thrown jars and may result from clay displacement during wheel work. The reasons for discarding the wasters were largely firing failures: warping and cracking from overfiring, loosened tripod legs and handles, and glazes accidentally fired in a reducing atmosphere. Taken together, the results portray a production tradition defined by both continuity and change, in which local potters favoured iron-rich, calcium-poor clay, tempered it with river sand, fired at low temperatures, and gradually adopted wheel-throwing and lead glazing, offering archaeologists a new quantitative template for reconstructing medieval craft knowledge and its transmission.

Subject of Research: The production technology and chaîne opératoire of medieval greyware and redware ceramics from 12th to 15th century Utrecht, the Netherlands

Article Title: Advancing the chaîne opératoire analysis of medieval greyware and redware ceramics: A case study from 12th to 15th centuries CE Utrecht, the Netherlands

Article References: Borgers, B., Gait, J., Bajnok, K., Allepuz, E. T., Bajnóczi, B., Len, A., & Griffioen, A. (2026). Advancing the chaîne opératoire analysis of medieval greyware and redware ceramics: A case study from 12th to 15th centuries CE Utrecht, the Netherlands. Archaeological and Anthropological Sciences, 18(9), Article 194. https://doi.org/10.1007/s12520-026-02554-x

Image Credits: AI Generated

DOI: 10.1007/s12520-026-02554-x

Keywords: medieval pottery, Utrecht, chaîne opératoire, ceramic technology, greyware, redware, small-angle neutron scattering, lead glazes, petrography, X-ray fluorescence, pottery workshops, the Netherlands