This systematic investigation of bioapatite, the mineral component of human bone, aims to characterize its crystallographic state, including lattice parameters and average crystallite size, and correlate these values with respect to anatomical position (bone function), physicality, and bone chemical composition. In sample sets of buried bone from three different human adult skeletons, anatomical variation of crystallographic parameters and correlation to chemical composition were indeed observed. In general, the observed bioapatite a unit-cell edge-length among all analyzed human bones in this study was larger by 0.1–0.2% compared to that of stoichiometric hydroxylapatite (HAp), and substantially larger than that of fluorapatite (FAp). Across all analyzed samples, the a (=b) lattice parameter (unit cell edge-length) varies more than does the c lattice parameter. Average crystallite size (average coherent diffracting domain size) in the c-direction was equal to approximately 25 nm, ranging among the analyzed 18 bone samples from about 20–32 nm, and varying more than crystallite size in the a,b-direction (~8–10 nm). Neither lattice parameters nor average bioapatite crystallite sizes appeared to be correlated with bone mechanical function. The relative chemical composition of the bone material, however, was shown to correlate with the a (=b) lattice parameter. To our knowledge, this research provides, for the first time, the systematic study of the crystallographic parameters of human bone bioapatite in the context of anatomical position, physical constitution, and bone chemical composition using X-ray powder diffraction (XRPD) and Fourier transform infrared spectroscopy (FTIR).

Struvite (MgNH₄PO₄·6H₂O) is a potential fertilizer mineral that can be obtained from wastewaters. When the ambient temperature changes, struvite may decompose in water and other phosphate-bearing minerals form instead. The wet decomposition may include complex mineralization, as the struvite crystal structure releases both water molecules and ammonia. An in-situ x-ray measurement for the wet transformation of the struvite is needed to get insight into the mineral formed and into the influence of the water temperature on the decomposition/remineralization. In this study, the X-ray diffraction (XRD) sample holder containing struvite and water in a sealed condition was heated to temperatures of 55 to 120 ^OC for 24 h. Later the still sealed sample holder was exposed to the X-ray beam with the Debye-Scherrer transmission technique, and the diffraction pattern was analyzed by the XRD Rietveld method. With increasing temperature (< 100 ^OC), struvite first dehydrated to dittmarite (MgNH₄PO₄·H₂O). Moreover, a decomposition of struvite into an amorphous form of magnesium hydrogen phosphate has occurred as the XRD background increased dramatically and showed a structured profile with very broad intensity maxima. Furthermore, struvite transforms into dittmarite, newberyite, and bobierrite when the sample was heated above 100 OC. The outcome of this work is expected to add knowledge on the instability of struvite, which may occur in the fields of the wastewater treatment and in the bio-mineralization in the urine of animals and humans.

Chamid bivalves are marine organisms that live in high-energy environments and are cemented to hard substrates. To avoid shell damage, the organisms form thick, densely ornamented shells. Shell material consists of aragonite, and the ornamentation may be either aragonitic or calcitic. The latter can be developed as scaly spines, rows of blades, or comarginal, radial arched lamellae. We investigated biological crystal morphology and mode of assembly of Chama arcana and Chama gryphoides shells. Structural characteristics were obtained from electron backscatter diffraction (EBSD) measurements, complemented with laser confocal and BSE imaging. We found a wide range of crystal morphologies and sizes, ranging from irregularly shaped calcite and/or aragonite prisms to tiny and thin aragonite laths. We observed four different modes of crystal assembly patterns: 1. strongly interlocked dendritic calcite units forming the ornamentation blades; 2. aragonite laths arranged to lamellae forming the outer shell layer, the layer adjacent to the calcite; 3. aragonite laths arranged into blocks comprising inner shell layers or aragonitic ornamentations; and 4. shell portions consisting of aragonite prisms, structured in size and crystal orientation, at muscle attachment sites. These four different types of crystal arrangements were observed for the shells of the investigated chamid species; however, they had slightly different strengths of structuring and slight variations in crystal organisation. Additionally, we observed unique microstructural features in Chama shells: We report ornamentation crystals resembling idiomorphic calcite and novel, twinned entities found at the changeover between the aragonitic layers. We highlight and discuss these differences and anomalies in this contribution.