The stability of hauerite (MnS2) as compared to that of pyrite (FeS2) can be explained by the long Mn–S distance and departure from the typical pyrite-type structures. The structural differences of MnX2 compounds (X=S, Se, and Te) are the result of spin configurations that are different than those of other MX2 compounds; however, the arrangement of d-electrons and the size of the ions in MnX2 compounds do not clearly explain why Mn2+ in MnX2 does not exist as a low spin state. To investigate the structural differences of MnX2 compounds, we synthesized single-crystal MnTe2 and MnSe2 and performed single-crsytal X-ray diffraction experiments. The single-crystal X-ray diffraction experiments were conducted on MnTe2 [a=6.9513(1) Å, u-parameter=0.38554(2), space group Pa3̅, Z=4], MnSe2 [a=6.4275(2) Å, u-parameter=0.39358(2)], MnS2 [hauerite; a=6.1013(1) Å, u-parameter=0.40105(4), obtained from Osorezan, Aomori, Japan], and FeS2 [pyrite; a=5.4190(1) Å, u-parameter 0.38484(5), obtained from Kawarakoba, Nagasaki, Japan]. The X-ray intensity datasets of these compounds do not show any evidence of symmetry reduction. In MnS2, the S–S distance is 2.0915(8) Å, which is significantly shorter than that of FeS2 (2.1618(9) Å), and the mean square displacement of S (U11=0.00915(9) Å2) is smaller than that of Mn (U11=0.01137(9) Å2). The thermal vibration characteristics of MnX2 compounds are significantly different than those of FeS2. Based on structural refinement data, we discuss the low spin state of MnX2 compounds and the structural stability of pyrite-type structures.

The local structure around zinc atoms in Cretaceous-Tertiary (K-T) boundary clay from Stevns Klint, Denmark, was studied by Zn Kedge XAFS spectroscopy. XAFS measurements were performed at the BL-12C and BL-9C beamlines at the Photon Factory in the High Energy Accelerator Research Organization (KEK), Japan. The local structure around Zn in the K-T clay resembles the framework structure of the tetrahedral ZnO 4 site in the zinc silicate willemite, judging from first shell Zn-O and second shell Zncation distances [1.953(3) and 3.51(2) Å, respectively], Xray absorption near edge structure (XANES) spectra, and radial structure function. The Debye-Waller factor σ 2 of the K-T clay sample is similar to those for the tetrahedral sites in crystalline phases, where Zn occupies mainly tetrahedral sites. The local structure of Zn in the K-T clay is peculiar and differs from that found in many clay minerals.

The Ti and Zr K‐edge X‐ray absorption near edge structure (XANES) spectra of ATiO3 (A = Sr, Ba, and Pb) and PbZrO3 perovskite‐type compounds have been measured in the temperature range 20–900 K. Quantitative comparison is performed in a wide temperature range to clarify how the intensities of the pre‐edge peaks and shoulders change with temperature. In the ferro‐ and antiferroelectric tetragonal phases, the intensities of some of the peaks and shoulders decrease with increasing temperature and the peak‐top energies shift to the higher energy side. The shift can be explained by the position and decrease (increase for SrTiO3) of the D2 peak in the difference spectra. The peak‐top position of the pre‐edge peak in XANES does not always represent the true energy for independent transition to an orbital because several orbitals with similar energies overlap. The tetragonal SrTiO3 phase shows the same behavior as ferroelectric P4mm tetragonal BaTiO3 and PbTiO3 perovskite. The temperature dependence of the shoulder is also an important index. The presence of a phase with local polar tetragonal strain is important in materials and the Earth's constituent solid solutions. The existence of ferro‐ and antiferroelectricity can be determined by temperature‐dependent XANES measurements.

Petzite, Ag 3 AuTe 2 , crystallizes in the space group I4 1 32, which is a Sohncke type of space group where chiral crystal structures can occur. The structure refinement of petzite reported long ago [Frueh (1959). Am. Mineral. 44, 693-701] did not provide any information about the absolute structure. A new singlecrystal X-ray diffraction refinement has now been performed on a sample from Lake View Mine, Golden Mile, Kalgoorlie, Australia, which has resulted in a reliable absolute structure [a Flack parameter of 0.05 (3)], although this corresponds to the opposite enantiomorph reported previously. The minimum Te-Te distance is 3.767 (3) Å , slightly shorter than the van der Waals bonding distance, which suggests a weak interaction between the two chalcogens. XANES spectra near the Au and Te L III edges suggest that the chemicalbonding character of Au in petzite is more metallic than in other gold minerals.

The local structures of tektites and natural glasses were studied by Zr K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements in order to obtain quantitative data on the Zr-O (bonding) distances and coordination numbers for the glasses. Zr 4+ ions have different coordination environments. The structure of glass (tektite, impact-related glass, fulgurite, and volcanic glasses) is affected by the temperature during the glass-formation process. Differences in the formation processes for natural glasses result in different local structures for the zirconium ions.All tektites can be classified as being of the same type and as having 7-fold coordination Zr ions. The Zr-O distances in tektite glasses are 2.198-2.215 Å, and their XANES spectra are similar, too. Impact-related glasses can be classified into different types and are formed under different physical and geological processes at the impact event. Volcanic glasses, impact-related glasses, and fulgurite glasses have several local Zr structures with 6-and 7-fold coordinated Zr ions. It can thus be concluded that local structures of Zr in natural glasses are closely related to the formation temperature and quenching conditions of the glasses. The Zr XAFS spectra of natural glasses can be used to identify the naturalglasses.