How flakes shatter: a critical evaluation of quartz fracture analysis

Despite its worldwide use as a stone tool raw material, quartz is known to be a difficult material for archaeologists. The main reason for this is the tendency of quartz flakes to fragment during detachment, which complicates the use of traditional lithic analyses. In this article we present an experimental study of quartz flake fragmentation. We evaluate the method called fracture analysis that has been developed and used explicitly for the study of quartz assemblages. The method assumes high predictability of quartz flake fragmentation, but our experiments show that there is significant variation in fragmentation that fracture analysis does not take into account. Our results indicate that this variation is partly explained by indenter hardness, the relative thickness of the detached flake, as well as individual knapper-related factors. These results undermine the applicability of quartz fracture analysis in its current form. In addition, we discuss the effects of flake fragmentation on the technological organisation of prehistoric quartz users and suggest that it has affected reduction strategies as well as blank and tool dimensions. We also suggest that there should be mobility-related differences in archaeological assemblages in terms of the quality of the quartz raw material and that the curation of quartz should be low in relation to better quality raw materials used parallel with it.     

An empirical test of the relative frequency of bipolar reduction in Beds VI,V, and III at Mumba Rockshelter,Tanzania: implications for the East African Middle to Late Stone Age transition

Mumba Rockshelter, Tanzania, is the only East African site spanning a continuous record of more than 100,000 years, including the Middle Stone Age (MSA) to Late Stone Age (LSA) Transition. Rather than examine the presence or absence of traditional markers of “behavioral modernity”, we have endeavored here to respond to the calls of Shea (2011) and Basell (2008) by examining the proportional similarity of a trait present throughout the MSA–LSA sequence at Mumba Rockshelter: the bipolar technique of lithic reduction. We use a quantified, experimentally derived proxy to track the relative amount of bipolar percussion among Mumba's Beds VI, V, and III, namely, waste shatter. Our examination of Mehlman's previously unanalyzed collections from Mumba demonstrates that in terms of bipolar production Bed V is statistically indistinguishable from the Late Stone Age (LSA) Bed III, but significantly different from the Middle Stone Age (MSA) Bed VI. Given that Bed V dates to 56.9 ± 4.8 − 49.1 ± 4.3 ka cal BP, this result is consistent with other evidence that the origins of the LSA in East Africa began well before 40 kya, and that Mumba Bed V represents one of the earliest manifestations of the LSA in East Africa. We conclude with a discussion of factors that may have influenced the increased dependence of bipolar production at the site.     

A combined visual-geochemical approach to establishing provenance for pegmatite quartz artifacts

A technique for establishing source provenance for pegmatite quartz artifacts was developed using a quarry sample from the Churchill River basin of northern Manitoba and Saskatchewan. Secondary ion mass spectrometry (SIMS) was used to quantify Ti, Ge, Th, and U trace element concentrations and Pb isotope ratios, coupled with qualitative visual characteristics to distinguish between pegmatite quartz from different archaeologically exploited sources in the Churchill River basin region. The technique was also applied to a small sample of quartz artifacts recovered from sites in and around the study area in a preliminary attempt to assign or rule out raw material provenance to characterized sources.     

On the intrinsic accuracy and precision of luminescence dating techniques for fired ceramics

Luminescence dating techniques have been used extensively for archaeological and geological samples. Such techniques are based on thermally or optically stimulated signals. This paper presents simulations of several luminescence techniques for equivalent dose (ED) estimation for ceramic materials containing quartz. The simulations are carried out using a recently published comprehensive kinetic model for quartz, consisting of 11 electron and hole traps and centers. The complete sequence of the experimental protocols for several thermoluminescence (TL) and optically stimulated luminescence (OSL) techniques are simulated using the same set of kinetic parameters. The specific simulated protocols are: additive dose TL protocol, predose technique (both additive and multiple activation versions), phototransfer protocol, single aliquot regenerative optically stimulated luminescence (SAR-OSL) protocol, and SAR thermoluminescence protocol (SAR-TL). One hundred random variants of the natural samples were generated by keeping the transition probabilities between energy levels fixed, while allowing simultaneous random variations of the concentrations of the 11 energy levels. The relative intrinsic accuracy and precision of the protocols are simulated by calculating the equivalent dose (ED) within the model, for a given natural burial dose of the sample. The intrinsic accuracy of these techniques is estimated by simulating natural irradiation of the samples with a known burial dose, followed by simulation of the luminescence method used to recover the estimated dose ED. The percent difference between the burial dose and the ED value represents the simulated accuracy of the luminescence technique. The relative intrinsic precision of these techniques is estimated by fitting Gaussian probability functions to the ED values obtained with the 100 model variants. It is found that the various techniques can reproduce natural paleodoses in the range 10 mGy–10 Gy with a typical intrinsic accuracy of +1 to 10%. Techniques based on single aliquot protocols were found in general to be more precise than techniques requiring the use of multiple aliquots. In addition, techniques based on interpolation of experimental data were found to be consistently both more precise and accurate than those based on extrapolation of experimental data.     

Development of quartz cathodoluminescence for the geological grouping of archaeological ceramics: firing effects and data analysis

Cathodoluminescence (CL) spectrometry reveals genetic crystallographic and chemical characteristics of quartz grains specific to the thermodynamic conditions in which they crystallised and their mineralisation history. These genetic characteristics have been used successfully to determine the provenance of sediments. Geological sediments are the raw material for archaeological ceramics which means quartz CL has a potential application in ceramic provenance studies, particularly for fine wares and fabrics in which quartz is the only identifiable inclusion.     

The origins of two purportedly pre-Columbian Mexican crystal skulls

The well-known life-size rock crystal skull in the British Museum was purchased in 1897 as an example of genuine pre-Columbian workmanship, but its authenticity has been the subject of increasing speculation since the 1930s. This paper is concerned with the history, technology and material of the skull and another larger white quartz skull, donated recently to the Smithsonian Institution. Manufacturing techniques were investigated, using scanning electron microscopy to examine tool marks on the artefacts, and compared with Mesoamerican material from secure contexts. A Mixtec rock crystal goblet and a group of Aztec/Mixtec rock crystal beads show no evidence of lapidary wheels. They were probably worked with stone and wood tools charged with abrasives, some of which may have been as hard as corundum. Textual evidence for Mexican lapidary techniques during the early colonial period, supported by limited archaeological evidence, also indicates a technology without the wheel, probably based on natural tool materials. In contrast, the two skulls under consideration were carved with rotary wheels. The British Museum skull was worked with hard abrasives such as corundum or diamond, whereas X-ray diffraction revealed traces of carborundum (SiC), a hard modern synthetic abrasive, on the Smithsonian skull. Investigation of fluid and solid inclusions in the quartz of the British Museum skull, using microscopy and Raman spectroscopy, shows that the material formed in a mesothermal metamorphic environment equivalent to greenschist facies. This suggests that the quartz was obtained from Brazil or Madagascar, areas far outside pre-Columbian trade networks. Recent archival research revealed that the British Museum skull was rejected as a modern artefact by the Museo Nacional de Mexico in 1885, when offered for sale by the collector and dealer, Eugène Boban. These findings led to the conclusion that the British Museum skull was worked in Europe during the nineteenth century. The Smithsonian Institution skull was probably manufactured shortly before it was bought in Mexico City in 1960; large blocks of white quartz would have been available from deposits in Mexico and the USA.     

Using Optical Coherence Tomography to Examine Additives in Chinese Song Jun Glaze

We use optical coherence tomography (OCT) to acquire microstructure images of Chinese Song Jun glaze to reveal the copper and quartz additives used and, in two typical samples, we show that the amount added is considerable. Focusing on these two additives, including the species, amount and granule (particle) size added in the glaze, the objective of the present study is to explore how they functioned in relation to the Jun glaze's visual characteristics, opalescence and sky‐blue colour, attributed to the unique liquid–liquid phase separation that occurs in Jun glaze.     

An Experimental Investigation into the Accidental Invention of Ceramic Glazes

Glazed objects, mainly in the form of glazed quartz and steatite solid stones, first appeared during the fifth millennium bc . At the present time, it is generally accepted that the accidental discovery of glazing was associated with ancient copper production. However, the replication experiments already conducted on glazed stones were unable to provide a convincing explanation for the accidental invention of ceramic glazes. This paper attempts to suggest a possible explanation for the accidental invention of glazes on solid stones (i.e., steatite and quartz) during the Chalcolithic period. A series of replication experiments were undertaken and the resulting objects were examined using SEM–EDS.     

Subterranean transport and deposition of quartz by ants in sandy sites relevant to age overestimation in optical luminescence dating

An artificial layered sandy site was created using a combination of native sand and colored sand (3 parts native uncolored quartz, 1 part colored quartz) in Apalachicola National Forest near Tallahassee, Florida. Twelve layers of sand, each 1 by 1 m in horizontal extent by 10 cm in thickness were emplaced to a depth of 2 m followed by implantation at the surface of a Florida harvester ant (Pogonomymrex badius) colony (the lower two layers were 50 cm thick). The colony excavated a nest, and after 7 months, the sand layers were excavated to the base to test the hypothesis that sand grains were moved upward within the ant nest without reaching the surface. The ants penetrated 11 of the 12 colored layers reaching a depth of 130 cm. Thirty nine sticky-acetate peels of ant chamber floors were collected and colored sand grains were counted under a microscope. More than 16,000 grains were identified in layers that did not originally host them. Of these, more than 80% were unambiguously moved upward. This means that possibly as many as 54,000 upwardly mobile grains were present (ratio of 3:1 uncolored to colored). In relation to optical luminescence (OSL) dating, this means that grains that would not have been optically zeroed by transport to the surface (defined here as subterranean-transported) were present in abundance, and that if the site was ancient, there would have been found many grains that were older than the layers they presently reside in, even if only one colony of harvester ants had disturbed the layers. This is in addition to the fact that backfilling of chambers and tunnels may contribute even more significantly to the presence of a subterranean-transported component of an OSL sample. We conclude that ants can significantly affect the age distributions in sandy archaeological sites. Multiple examples of such disturbances have been documented in the literature. Most relevant to our results are recent studies of the OSL chronology of Pre-Clovis-age and Palaeoindian age archaeological sites in sandy environments in North America that may have been compromised by ant bioturbation of quartz sand grains. Here we have examined in detail the potential effects of one episode of ant nest-building on the age overestimation of affected sediments. From this we found that as few as 12 episodes of bioturbation involving backfilling of chambers in the same volume of sand could lead to the presence of 1 contaminant grain per 50 grains of sample.     

Mixed occupation during the Middle Palaeolithic: Case study of a small pit-cave-site of Les Pêcheurs (Ardèche,south-eastern France)

The Pêcheurs cave is a unique example of a Middle Palaeolithic site with three kinds of accumulations: (1) ibex that died in a natural trap, (2) carnivores that died within the cavity, and, (3) a series of short-term occupations by humans who left a few artifacts and a hearth area. Biological patterns of ibex remains (skeletal parts, age) show a homogeneous structure, related to natural death inside the cave. The Chassezac valley is narrow and sinuous, bordered by steep cliffs occupied by well-adapted hoofed-species (Caprinae). Moreover, Les Pêcheurs is a shallow cave, pit-like, and in its deepest part (Sector 4) provided both man and animals with shelter. The presence of a fire place (in the middle of the sequence of Sector 4) firmly indicates the presence of an in situ occupation by a small group of hominids. According to the stratigraphical patterns and the analysis of the lithic assemblages, artifacts do not seem to have been introduced into sediments. The lithic assemblages (technically homogeneous) indicate that small mobile human groups inhabited a cave that offered, by virtue of its morphology, a natural shelter against the cold winds blowing in the Chassezac valley and the plateaus of the south-eastern borders of the Massif Central Mountains. The exploitation of biotopes such as this rocky area constitutes a specific case of human subsistence behavior and settlement strategy. The deepest layer is characterized by a lithic assemblage mostly made of local raw material (quartz) implying a low investment in lithic production. Few flakes made from non-local flints attest to the mobility of the human occupants who moved across these areas and perhaps found in the valleys, short-term refuge.