Geometry of the four-circle diffractometry in the fixed φ mode was reexamined to revise control programs of the diffractometer for intensity measurements with high-pressure diamond-anvil cells. The benefit of the φ=0 mode has been explained on the basis of the fact that the sum of α_p (the angle between the incident X-rays and the radial symmetry axis of the diamond-anvils) and α_d (the angle between the diffracted X-rays and the radial symmetry axis of the anvils) becomes minimum. In the present studies, it was revealed that not only the sum of α_p and α_d, but α_p and α_d themselves are minimum when φ=0 or π. This elucidates the above benefit more easily and simply. Importance of the φ=π mode measurements was pointed out.

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The crystal structure of hollandite from Gowari Wadhona, India has been refined. Chemical formula determined by EPMA and moisture counter is (Ba_0.75K_0.38)_1.13 (Mn_7.85Fe_0.15)₈O₁₆·0.41H₂O. The structure is monoclinic, I2⁄m, and cell constants are a=10.006(3)Å, b=2.866(1)Å, c=9.746(2)Å, β=91.17(3)°. Each atom exists on a mirror plane.(y=0, or 0.50). Manganese atom is in octahedral coordination. MnO₆ octahedra are distorted and manganese atoms shift to unshared oxygens. The tunnel site is occupied by Ba²⁺, K⁺ and H₂O. These cations and molecules do not show continuous distribution along the tunnel but only one single peak is observed. This mineral gives an X-ray powder pattern different from that of tetragonal hollandite. The relationship between the site occupancies of tunnel cations and the powder diffraction intensities is discussed. As the occupancy of tunnel site increase, the intensity ratio of I(200)+I(002) to I(301)+I(-103) decreases.

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The structure of synthetic Rb_0.27MnO₂ has been determined by using the three dimensional single crystal X-ray data. The compound is monoclinic, space group A2⁄m, a=15.04[2]Å, b=2.886[2]Å, c=14.64[2]Å, β=92.4(2)°, and Z=14.
An initial model structure deduced from the structure of psilomelane (or romanéchite) was refined by employing 1415 independent reflections of |Fo|>3σ. The final R value is reduced to 0.122. The structure consists of the quintuple strings of MnO₆ octahedra which are linked by the double strings to form a 2×5 tunnel running in the b direction. A quadruple row of Rb ions occupys the tunnel. The electron densities of Rb ions show almost continuous distribution. The compound has four unequivalent MnO₆ octahedra with the mean Mn-O distances of 1.930(4), 1.937(4), 2.062(4) and 1.946(4)Å. The largest Mn(3)O₆ octahedron accomodates Mn³⁺ ion, being distorted by the Jahn-Teller effect. The rest of three octahedra accomodates Mn⁴⁺ ion. There is no clear evidence for Mn²⁺ ion.

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Legrandite and koettigite are found in an oxidized arsenopyrite-sphalerite ore from the Ogibira mine, Okayama Prefecture. They occur as secondary products in cavities and on fracture surfaces in compact limonite. Legrandite is commonly honey-yellow in color with a vitreous luster, and occurs as prismatic crystals or as radial aggregates. The crystals with length up to 3.5 mm show the forms a(100), m(110), c(001) and p(-111). It is monoclinic and the unit cell parameters are: a=12.789(5), b=7.916(2), c=10.218(3)Å and β=104.36 (3)°. Wet chemical analysis gave an empirical formula (Zn_1.90 Fe_0.06 Al_0.01 Ca_0.01 Na_0.02 K_0.01)_Σ2.01 (As_1.00 P_0.01)_Σ1.01 O_4.00 (OH)_1.00·1.00 H₂O. It is optically positive with refractive indices, α=1.700, β=1.708, γ=1.738 and 2V about 42°. Its physical properties are: Vichers microhardness 254–270kg/mm²(25g load), Mohs hardness 4.5, and density 3.98 g/cm³(meas) and 4.038 g/cm³ (calc).
Koettigite is pale blue to blue in color with a vitreous luster. The mineral mostly occurs as parallel aggregates with length up to 2 cm along [001]. It is monoclinic and the unit cell parameters are: a=10.249(4), b=13.449(4), c=4.759(2)Å and β=105.11(4)°. Wet chemical analysis gave an empirical formula (Zn_2.53 Fe_0.32 Al_0.01 Mg_0.01 Ca_0.01 Na_0.11 K_0.01)_Σ3.00 (AS_2.00 P_0.02)_Σ2.02 O_7.99·8.01 H₂O. It is optically positive with α=1.617, β=1.646, γ=1.680 and 2V=84°. Its physical properties are: Mohs hardness 2.5, density 3.23 g/cm³ (meas) and 3.240 g/cm³(calc). This mineral has perfect cleavage on {010}.

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Ardennite is found to occur in a piemontite-bearing quartz schist from the Asemigawa area in the Sanbagawa metamorphic terrain, central Shikoku. The ardennite-bearing quartz schist contains quartz, piemontite and garnet as major constituents with subordinate amounts of talc, chlorite, albite, calcite, hematite, braunite, rutile and apatite, together with ardennite. Ardennite is pale golden yellow and occurs as subhedral and prismatic crystals up to 1 mm in length. It is optically positive with 2V_Z=57±3°. It is orthorhombic and unit cell parameters are a=5.828(2) Å, b=18.540(8) Å, c=8.692(3) Å and V=939.1(6) ų. As₂O₅ and V₂O₅ contents of ardennite reach 10.8 and 1.3 wt.% in maximum, respectively. The empirical formula of the ardennite is (Ca_0.53Mn_3.67)(Mg_1.02Cu_0.03Fe_0.20³⁺Al_4.47Ti_0.01)(As_0.80V_0.09) Si_5.25O₂₂ (OH)₆. It is slightly poor in (As + V) and rich in Si compared with the ideal formula of ardennite. Piemontite contains SrO of 0.7wt.% in maximum.

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