The research team, led by Catarina Ermida of the Laboratory of Forensic Anthropology, together with Eugénia Cunha, Francisco Gil and Maria Teresa Ferreira, drew on a uniquely well-documented resource: identified skeletal collections in Portugal, including the 21st Century Identified Skeletal Collection at Coimbra and clavicles recovered from autopsies at the Portuguese National Institute of Legal Medicine and Forensic Sciences. Because the identities and death dates of these individuals are known with documented precision, the researchers could work with genuinely known postmortem intervals, something that is remarkably rare in this field. In total, 38 unburned human clavicles were analyzed, spanning PMIs from 4 to approximately 500 years. To probe the effects of heat, the team added a subsample of 12 clavicles that had been burned and carried a PMI of only four years, providing a natural experiment in how thermal alteration reshapes bone mineral independently of time.

The technique at the heart of the study, X-ray diffraction, is one of the workhorses of materials science. When a beam of X-rays strikes a crystalline substance, the atoms scatter the radiation in patterns dictated by the regular arrangement of the crystal lattice. Bone mineral, a poorly crystalline form of calcium phosphate closely related to the mineral hydroxyapatite, produces characteristic diffraction peaks. Freshly formed bone contains many small, imperfect, strain-laden crystals, and their disorder broadens and smears the diffraction peaks. As bone ages, and especially as it is altered by the burial environment, crystals tend to recrystallize and coarsen: small crystals dissolve and redeposit onto larger ones, lattice defects are repaired, and the peaks become taller, narrower and sharper. Two parameters capture this maturation. The crystallinity index, or CI, is calculated from the relative sharpness of the diffraction pattern, essentially a ratio comparing the height of key peaks with the depth of the trough between them. Crystallite size, meanwhile, is estimated from the broadening of the diffraction peaks themselves, using the physical principle that smaller crystals produce wider peaks. If bone mineral truly aged like a clockwork, both numbers should climb steadily with time since death.

That is roughly what the study found for the crystallinity index, but not for crystallite size. Across the 38 unburned clavicles, crystallite size showed no consistent relationship with PMI at all; values fluctuated widely from sample to sample, swamped by variability that had nothing to do with elapsed time. The crystallinity index told a different story. It displayed a moderate positive correlation with postmortem interval, with a Spearman rank correlation coefficient of 0.587, a statistically significant result with a p value below 0.001 and a 95 percent confidence interval stretching from 0.194 to 0.810. In plain terms, older bones did tend, on average, to show sharper, more crystalline diffraction patterns, consistent with the long-standing picture of slow diagenetic recrystallization. For archaeologists sorting ancient from modern material, that trend is real and useful. But the confidence interval also reveals how noisy the relationship is, and the devil, as so often in forensic science, was hiding in the scatter.

That scatter is precisely what limits the forensic dream. The authors observed substantial overlap in crystallinity values within the forensic timescale, meaning that a bone dead for five years might produce a CI indistinguishable from one dead for twenty or thirty years. Samples with identical known PMIs returned markedly different crystallinity values, a pattern the researchers attribute to taphonomic factors, the full suite of environmental insults that a body experiences after death: soil chemistry, moisture, pH, temperature swings, microbial attack, roots, and drainage. Two skeletons buried for the same number of years in different microenvironments can follow very different diagenetic trajectories, so the mineral fabric they present to an X-ray beam reflects burial history as much as burial duration. In forensic casework, where the difference between a recent death and a decades-old one can determine whether a crime is prosecuted, that ambiguity is decisive. A method that produces overlapping values across the critical range cannot pin a date, only gesture at one.

The burned-bone subsample added a further warning. Heat is known to drive dramatic recrystallization in bone mineral: as temperatures rise during burning, the small bioapatite crystals grow, merge and reorganize, sharpening diffraction patterns dramatically. The 12 burned clavicles in the study, all with a PMI of just four years, showed thermal alteration of crystallinity that could, in effect, mimic the signature of much older remains. A forensic investigator who analyzed a burned recent bone and interpreted its high crystallinity as a sign of antiquity would be badly misled. Conversely, cremated archaeological material could masquerade as fresh if the thermal signature were misread. The study’s authors stress that thermal history must be recognized and accounted for before any crystallinity measurement is interpreted as a proxy for time, and their data demonstrate concretely how fire can scramble the clock that X-ray diffraction is meant to read.

None of this means X-ray diffraction is useless in forensic contexts. The technique is fast, relatively inexpensive, minimally destructive, and its parameters do track genuine postmortem change in bone mineral. The crystallinity index’s moderate correlation with PMI confirms that mineral maturation is a real, measurable phenomenon, and the study’s use of documented skeletal collections shows how such measurements can be calibrated against known truth rather than assumed ages. What the findings deflate is the more ambitious claim: that CI or crystallite size alone can deliver a precise postmortem interval. The results align with a growing body of literature that has tested physicochemical dating proxies, from earlier X-ray diffraction studies to spectroscopic approaches, and found the same recurring pattern, a broad correlation with time that dissolves into scatter exactly where forensic questions need resolution. The authors conclude that, although XRD-derived crystallinity parameters provide useful insights into postmortem changes in bone mineral structure, their application for PMI estimation remains limited.

There is a broader lesson here about how forensic science progresses, and it is one worth savoring. The temptation in a young and under-resourced field is to chase a single magic number, a lone chemical or crystallographic readout that solves the dating problem once and for all. This study, grounded in 50 human clavicles with known histories, shows why that chase so often disappoints: death does not happen in a laboratory, it happens in soil, in water, in fire, and in a thousand uncontrolled environments that each rewrite the bone record in their own way. The measured effect of time is real but entangled with the effects of everything else. Progress will likely come not from a solitary indicator but from combinations of methods, larger and better-documented reference collections, and models that explicitly incorporate taphonomic variables rather than wishing them away.

For now, the crystals in our bones keep their secrets stubbornly. They do grow and ripen after death, and a diffractometer can watch it happen. But between a fresh forensic case and a centuries-old skeleton, the crystalline clock runs at different speeds in different graves, and fire can knock its hands sideways entirely. The Coimbra team’s careful negative result is, in its way, as valuable as a breakthrough: it tells every future investigator exactly where the limits lie, and redirects the hunt for the forensic clock of death toward approaches humble enough to respect the chaos of the burial world. Until then, the question of how long ago someone died will continue to demand the oldest tools of all, careful context, cautious inference, and the accumulated judgment of forensic anthropologists who know that every bone tells more than one story.

Subject of Research: X-ray diffraction analysis of bone mineral crystallinity as a potential marker of the postmortem interval in human skeletal remains

Article Title: X-ray diffraction analysis of bone crystallinity and its association with postmortem interval in human skeletal remains

Article References: Ermida, C., Cunha, E., Gil, F., & Ferreira, M. T. (2026). X-ray diffraction analysis of bone crystallinity and its association with postmortem interval in human skeletal remains. International Journal of Legal Medicine. https://doi.org/10.1007/s00414-026-04020-8

Image Credits: AI Generated

DOI: 10.1007/s00414-026-04020-8

Keywords: X-ray diffraction, bone crystallinity, postmortem interval, forensic anthropology, human skeletal remains, crystallinity index, crystallite size, taphonomy, bone diagenesis, burned bone, time since death, International Journal of Legal Medicine

The sample comprised 297 non-adults and 793 adults, including 258 males, 244 females and 291 individuals of undetermined sex. Sex was estimated from the morphology of the innominate bones, cranium and mandible using standard anthropological criteria, applied only to individuals older than 15 because secondary sexual characteristics develop after puberty. Age at death in adults was reconstructed through a battery of well-established skeletal indicators, including the pubic symphysis, auricular surface of the ilium, acetabulum, ectocranial suture closure, sternal rib ends, the sternal end of the clavicle and patterns of dental wear. For non-adults, the researchers relied on the formation and fusion of ossification centers, the diaphyseal lengths of long bones and tooth eruption sequences. Individuals with severe skeletal pathologies capable of distorting body proportions, such as rickets, were excluded from stature and body mass analyses, whereas those with milder conditions such as osteoarthritis were retained.

Life expectancy at birth was calculated using a stationary population life table based on Halley’s model, an approach the authors selected because the burial assemblages reflect attritional rather than catastrophic mortality and because the method permits direct comparison with a substantial body of published paleodemographic research from the Iberian and Italian peninsulas. Stature was estimated with Pearson’s regression equations, derived from the physiological lengths of the left femur and tibia, chosen because the French reference sample is biologically and geographically the closest match to Mediterranean populations and has been shown to perform well on Spanish and Italian skeletal series. Body mass was derived from the femoral head diameter using equations developed by Ruff and colleagues, a well-validated proxy because the femoral head remodels in response to weight-bearing loads. Body mass index was then computed as body mass divided by the square of stature, with individuals classified as underweight, normal weight, overweight or obese according to conventional BMI thresholds. Statistical comparisons between the sexes employed Student’s t-tests or Mann-Whitney U tests depending on the distribution of the data, while temporal trends were tested with one-way ANOVA followed by Tukey post-hoc comparisons, all conducted in SPSS at a significance threshold of p < 0.05.

The results reveal a striking asymmetry between the four biological indicators. Life expectancy at birth remained relatively stable across most periods, hovering between roughly 21 and 27 years, before showing a marked increase during the Modern period. The Prehistoric value of just over 12 years is exceptionally low, but the authors caution that the small Prehistoric sample of 45 individuals, shaped by funerary practices such as adult cremation in the Late Bronze and Iron Ages, likely depresses this figure far below any biological reality. The Roman period yielded a life expectancy of about 21.6 years, squarely within the range documented for ancient Mediterranean populations, where nearly half of all children may have died before age five. Life expectancy peaked at approximately 27.2 years in Late Antiquity, dipped to about 25 years during the turbulent Medieval centuries, and climbed again to 27.15 years in the Modern period.

Stature, by contrast, displayed no statistically significant variation across the seven millennia under study. Male averages ranged narrowly between 164 and 166 centimeters, and female averages between 151 and 154 centimeters, in every period analyzed. Males were significantly taller than females throughout, as expected from sexual dimorphism, but the constancy of absolute height across such dramatic cultural transformations, from Neolithic farming villages to the proto-industrial city, surprised the researchers. The finding parallels a comparable diachronic study of Milan, and the authors suggest that restricting the analysis to a single urban area minimizes the confounding effects of geography, microclimate, agricultural systems and economic activity that have produced the U-shaped stature trends reported in earlier studies that mixed rural and urban, and multi-regional, samples.

Body mass and body mass index told a very different story, showing statistically significant changes over time in both sexes. In the Prehistoric assemblage, virtually all individuals fell within the normal weight range, with only about 14 percent of males classified as overweight and no underweight or obese individuals at all. Overweight cases rose during the Roman period to roughly 30 percent of males and 29 percent of females. Obesity made its first appearance in the archaeological record of Barcelona during Late Antiquity, detected in about 1 percent of females, alongside the earliest underweight individuals. During the Medieval period, male body mass dropped to its lowest recorded average of 59 kilograms, and underweight classifications climbed to over 19 percent of males, a pattern the authors link to famines, warfare, sieges and epidemic disease that plagued the city between the ninth and fourteenth centuries.

The Modern period brought a decisive reversal. Body mass peaked in both sexes, and overweight prevalence surged to 47 percent of males and 40 percent of females, the highest levels in the entire sequence. The authors attribute this shift to profound dietary and lifestyle transformations accompanying the transition from the pre-industrial to the industrial era: the Columbian Exchange introduced American crops such as maize and potatoes into the diets of the poor, proto-industrialization and textile manufacturing spurred economic recovery by the eighteenth century, and Spain experienced declining mortality thanks to improved nutrition, hygiene and disease treatment. Notably, the estimated body masses of Modern-period Barcelonans, averaging 67.6 kilograms for males and 59.5 kilograms for females, closely match those of post-medieval Dutch urban populations from Arnhem and Zwolle, underscoring a shared European trajectory of increasing body size in urban settings.

The study’s demographic data also captured the scars of Barcelona’s most catastrophic episodes. The Medieval decline in life expectancy, body mass and BMI coincides with centuries of conflict along the Spanish March between Islamic and Christian forces, recurrent famines, the devastating sack of the city by Almanzor’s army in 985, in which much of the population was killed or enslaved, and repeated outbreaks of the Black Death in the fourteenth century that decimated the population by as much as 40 percent. The city required roughly two centuries to recover its pre-1348 population levels. Violence against marginalized communities, including the destruction of the Jewish neighborhood of El Call, further marked this grim chapter. These historical events, the authors argue, left measurable imprints on the biological record, demonstrating that social inequality, conflict and epidemics translate directly into skeletal evidence of stress and mortality.

A central conclusion of the work is that life expectancy, body mass and body mass index proved far more sensitive to sociocultural and environmental change than stature did. While the skeleton preserved height with remarkable stability, the other three parameters registered three major shifts: the transition from Prehistory to the Roman period, a pronounced downturn during the Medieval era, and a strong recovery between the Medieval and Modern periods. Because the necropolises sampled predominantly contain individuals of lower socioeconomic status, buried in simple earth-cut graves rather than costly chapel tombs, the dataset offers a consistent window into the living conditions of ordinary working Barcelonans, from skilled tradesmen such as carpenters and weavers to unskilled laborers, across nearly seven millennia.

The authors acknowledge the inherent limitations of paleodemographic reconstruction, including the “osteological paradox,” the chronological gap between the Neolithic and Bronze Age assemblages, and the scarcity of comparable body mass data from other historical Spanish populations. Nevertheless, the study establishes a foundational reference framework for future diachronic bioarchaeological research in the Iberian Peninsula and contributes to a broader scientific conversation about how human biology, environment and history intertwine. It also carries a contemporary resonance: obesity, once entirely absent from the city’s dead, now ranks among its most pressing public health challenges, and the skeletal record makes clear that this epidemic is a product of the modern era’s abundance and sedentary living, not a feature of the human condition.