Through a correlative analytical approach encompassing backscattered electron scanning electron microscopy (BSE-SEM), energy dispersive X-ray spectroscopy (EDX), and micro-Raman spectroscopy, the composition of the mineralized biofilm around a dental implant, retrieved due to peri-implantitis, was investigated. The mineralized biofilm contains two morphologically distinct regions: (i) bacteria-containing zones (Bact+), characterized by aggregations of unmineralized and mineralized bacteria, and intermicrobial mineralization, and (ii) bacteria-free zones (Bact−), comprised mainly of randomly oriented mineral platelets. Intramicrobial mineralization, within Bact+, appears as smooth, solid mineral deposits resembling the morphologies of dental plaque bacteria. Bact− is associated with micrometer-sized Mg-rich mineral nodules. The Ca/P ratio of Bact+ is higher than Bact−. The inorganic phase of Bact+ is carbonated apatite (CHAp), while that of Bact− is predominantly octacalcium phosphate (OCP) and whitlockite (WL) inclusions. Compared with native bone, the inorganic phase of Bact+ (i.e., CHAp) exhibits higher mineral crystallinity, lower carbonate content, and lower Ca/P, C/Ca, Mg/Ca, and Mg/P ratios. The various CaPs found within the mineralized dental biofilm (CHAp, OCP, and WL) are related to the local presence/absence of bacteria. In combination with BSE-SEM and EDX, micro-Raman spectroscopy is a valuable analytical tool for nondestructive investigation of mineralized dental biofilm composition and development.

Hydrothermal conversion of single crystals of calcite, CaCO3, dolomite, CaMg(CO3)2, and magnesite, MgCO3, was carried out in ammonium phosphate buffer solution. While calcite easily forms a pseudomorph of hydroxylapatite, Ca5(PO4)3OH, it takes several weeks to convert magnesite into pseudomorphic dittmarite, (NH4)Mg(PO4)·H2O. The conversion of dolomite, as the compositional intermediate, also proceeded slowly, but yielded a biphasic pseudomorph composed of whitlockite, Ca9Mg(PO4)6O(PO3OH), and dittmarite. To our knowledge, this is the first description of a biphasic pseudomorph with chemically and structurally different phases. Near the surface, the two phases formed a porous layered structure, while towards the core of the single crystal a fine-grained mixture of both minerals precipitated. The initially sequential pattern of precipitation of Ca-rich whitlockite followed by Mg-rich dittmarite can be explained by dissolved Mg ions being adsorbed onto the dolomite surface or incorporated into hydrated magnesium complexes, retarding crystallization of dittmarite. Surface adsorbed Mg ions impeding further dissolution of dolomite also partly accounts for the observed lower reaction rates of dolomite and magnesite, as compared to calcite. An additional factor decreasing the reaction rates of dolomite and magnesite is a considerable increase in molar volume upon conversion, which restricts the formation of porosity and, hence, ion transport to the reaction front.

Phosphatic limestones and a related soil were described from collections made by the first Royal Society coral-reef-boring expedition to Funafuti in 1896 (Cooksey, 1896; David and Sweet, 1904, Judd, 1904; Sollas, 1904; cf. Cullis, 1904). Although there is some geographic uncertainty about the source of some of Judd's samples, the specimens came from three localities on Funafuti, the largest being on Amatuku.

Novel compounds Ca8−xPbxZnBi(VO4)7 (0 ≤ x ≤ 1.5) solid solution with the whitlockite-type structure were synthesized by a standard solid-state method. The unit-cell parameters were determined by X-ray powder diffraction and using Le Bail decomposition. The crystal structural of Ca6.5Pb1.5ZnBi(VO4)7 was refined by Rietveld method. It is found that Pb2+ cations occupy a half of the M3 site, whereas the M1 and M2 sites are predominantly occupied by calcium with admixture of Bi3+ cations. The M5 site is fully occupied by Zn2+ cations. The M4 site in the structure of studied sample remains vacant and does not participate in the cations arrangement. Optical second harmonic generation demonstrates high non-linear optical activity. Dielectric investigations confirm polar space group R3c. Changes in the non-linear optical and ferroelectric parameters are matched with lead and zinc cation distribution over the sites of the whitlockite-type structure.

The system of phosphates Ca9−xPbxHo(PO4)7 were obtained by solid-state reaction and were found to be isotypic with whitlockite-type β-Ca3(PO4)2 (polar space group R3c). The crystal structure encloses five crystallographic sites M1–M5 different in size and oxygen coordination. The unit-cell parameters were determinate using Le Bail decomposition. Rietveld method structural refining showed that Ho3+ ions are located statistically with calcium in M1 and M2 sites, while Pb2+-ions are located in the M3 site. Examination of optical second-harmonic generation evidences non-linear optical activity and confirms polar space group R3c. Structural mechanisms and dielectric features of phase transitions are strongly influenced by the exact distributions of atoms over the crystallographic sites.

New Ca8−xPbxCdBi(VO4)7 with the whitlockite-type structure were prepared by a standard solid-state method in air. Le Bail decomposition was used to determine unit-cell parameters. Structural refining was carried out by Rietveld's method. It is found that Bi3+ cations located partially in M1 and M2 sites along with calcium, while M3 site is settled in half by Pb2+-ions. Second-harmonic generation demonstrate highest non-linear optical activity and along with dielectric investigations indicate polar space group R3c.

New phosphates Ca9–xPbxEu(PO4)7 were obtained by solid state reaction techniques at 1213–1253 K in air atmosphere and were found to be isotypic with whitlockite-type β-Ca3(PO4)2. The unit cell parameters were determinate using Le Bail decomposition. Rietveld method structural refining showed that Eu3+ ions are located statistically with calcium in M1, M2, and M3 sites, whereas Pb2+-ions are preferentially located in the M3. Examination of optical second harmonic generation evidences nonlinear optical activity and confirms polar space group R3c.