Hanawaltite, ideally Hg1+6Hg2+O3Cl2, is orthorhombic, Pbma (57), with unit-cell parameters refined from powder data: a=11.790(3), b=13.881(4), c=6.450(2) Å, V=1055.7(6) Å3, a:b:c =0.8494:1:0.4647, Z=4. The strongest six lines of the X-ray powder-diffraction pattern [d in Å (I)(hkl)] are: 5.25 (80)(111), 3.164 (60)(231), 3.053 (100)(041), 2.954 (70)(141), 2.681 (50)(401), and 2.411 (50)(232,341). The mineral is an extremely rare constituent in a small prospect pit near the long-abandoned Clear Creek mercury mine, New Idria district, San Benito County, California. It was found on a single-fracture surface where it is intimately associated with calomel, native mercury, cinnabar, montroydite, and quartz. Individual crystals are subhedral to anhedral, platy to somewhat bladed, and average about 50 μm in longest dimension. The largest known crystal is approximately 0.3×0.3 mm in size and is striated parallel [001]. Hanawaltite is opaque to translucent (on very thin edges), black to very dark brown–black in color, with a black to dark red–brown streak. Other physical properties include: metallic luster; cleavage {001} good; uneven fracture; brittle; nonfluorescent; H<5; calculated density (for the empirical formula) 9.51 g/cm3.

In polished section, hanawaltite is moderately to strongly bireflectant and is pleochroic white (RI) to blue–white (R2). In reflected plane-polarized light, it is white with orange–red internal reflections in very thin grains and at grain margins. The anisotropy is strong with bright metallic blue rotation tints. Measured reflectance values, in air and in oil, are tabulated. Electron-microprobe analysis yielded Hg2O 82.46, HgO 14.27, Cl 3.33, H2O [0.34], sum [100.40], less O=Cl 0.75, total [99.65] wt. %, corresponding to Hg1+6.00Hg2+1.00 [Cl1.43(OH)0.57]Σ2.00O3.00, based on O+Cl=5. After the crystal structure was determined, the original microprobe value for Hg2O, 96.2, was partitioned in a ratio of 6Hg2O:HgO and (OH) was calculated, such that Cl+(OH)=2. The hanawaltite structure consists of undulatory [Hg–Hg]2+ ribbons which roughly parallel (100). The diatomic [Hg–Hg]2+ groups have anion tails which, in turn, serve as cross linkages between dimer ribbons through [Hg2+O2Cl2] planar rhombs. The structure is compared to that of other mercury oxychlorides and each is found to have its own unique structural features. This structural diversity is attributed to the inherent ability of mercury to adopt either metallic or ionic types of bonds. The mineral name honors the late Dr. J. D. (Don) Hanawalt (1903–1987), who was a pioneer in the field of X-ray powder diffraction.

The title materials are stuffed cristobalites possessing moderate to extreme pseudosymmetry. On the bases of their X-ray powder diffraction patterns, the Mg, Zn, and Cd compounds had been previously reported as cubic and, more recently, the Zn phase as orthorhombic. Newly measured X-ray powder diffraction data demonstrate that all (including the hitherto unknown Co analog) have the Pca21 structure of Na2BeSiO4 at room temperature, but with a widely variable degree of cubic pseudosymmetry. Observed X-ray diffraction data are in good agreement with those calculated by the Rietveld method using a constrained model with Pca21 M2+/Si site occupancy and pseudocentrosymmetric Pcab atom locations. For the most nearly cubic phase, the Cd compound, there is too little deviation in the pattern from cubic symmetry to support atom coordinate refinement even with the constrained model. In these derivatives of the stuffed cristobalite structure family, M2+ and Si atoms form an ordered tetrahedral array which avoids M2+–O–M2+ connections. Potassium atoms fill all of the intervening large cavity sites.

Crystal and X-ray powder diffraction data are presented for BaPbO3. The powder pattern was indexed and refined on an orthorhombic cell with a=6.0264(3)Å , b=8.5078(3)Å , c=6.0629(2)Å, Z=4, space group Imma. The phase may actually be monoclinic with space group I2/m, but no distortion from the orthorhombic cell was evident in the powder patterns, suggesting a β angle very close to 90.0°.

Improved powder XRD patterns for the titanium suboxides, TinO2n−1 (4≤n≤9), have been calculated from published single-crystal structures. To provide the best match with experimental data, the entire diffraction traces were simulated, and d-spacings and intensities extracted in the same manner as from experimental traces. The accuracy of the new patterns has been verified by comparison with measured powder patterns, particularly in the case of the n=4 and n=5 compounds where single-phase powders can be prepared relatively easily. Difficulties experienced preparing higher homologues have been related to the thermodynamic properties of this system.