An intermediate mineral between original type dachiardite and sodium-rich dachiardite has been found from Hatsuneura, the Ogasawara Islands. New data for dachiardite from the Onoyama mine, Kagoshima Pref., are also given. Based on the data for the above two dachiardites and literature data, mode of occurrence, chemical composition, optical, X-ray and thermal properties of dachiardite group zeolites were examined. The wide variation of chemical composition in this group seems to be due to the substitution of NaNa for Ca among the exchangeable cations with apparently independent substitution of Al for Si in the framework. The X-ray powder diffraction patterns are not distinguishable among the dachiardite group zeolites, and structural disorder is commonly observed in them. Correlation between Si/(Al+Fe³⁺) ratio and β angle is recognized. Refractive indices, 2V and c∧Z are closely related to R²⁺⁄(R⁺+R²⁺) ratio, in which R²⁺ and R⁺ are numbers of divalent and monovalent exchangeable cations, respectively. Some differences are recognized in TG-DTA curves and thermal stability between the original type dachiardite and the sodium-rich dachiardite. The results suggest that the isomorphous substitution may be expected in the dachiardite group zeolites.

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Taneyamalite is triclinic, space group P1 or P-1, unit cell parameters: a=10.1882±0.0012, b=9.7544±0.0006, c=9.5674±0.0011 Å, α=90.429°±0.019°, β=71.025°±0.014°, γ=109.168°±0.007°, V=844.03±0.13 ų, Z=1. Principal powder lines (d in Å) with relative intensities and indices are: 9.155(100) (010), 7.948(22) (-110), 4.578(15) (020), 3.614(13) (120), 3.252(37) (-130), 3.067(17) (-230), 2.774(24) (220), 2.665(18) (3-13), 2.202(21) (230), 1.696(17) (5-43), 1.686(12) (150). Wet chemical analysis gives: SiO₂ 40.32, TiO₂ 0.05, Al₂O₃, 2.08, Fe₂O₃ 8.68, FeO 11.88, MnO 23.83, MgO 2.50, CaO 0.53, Na₂O 1.63, K₂O 0.10, H₂O⁺ 6.99, H₂O⁻ 0.73, total 99.32%, corresponding to (Na_0.91Ca_0.16K_0.04)_Σ1.11 (Mn²⁺₅₀₇₈Mg_1.07Fe²⁺_2.85Fe³⁺_1.87Al_0.26)_Σ11.83 (Si_11.55 Al_0.44 Ti_0.01)_Σ12.00(O_30.63 (OH)_13.37)_Σ44.00 on the basis of O+OH=44. The ideal formula is (Na, Ca) (Mn²⁺, Mg, Fe²⁺, Fe³⁺, Al)₁₂ (Si, Al)₁₂ (O, OH)₄₄, where Na and Mn²⁺ are the most dominant species in the respective sites. Therefore, taneyamalite is a Mn²⁺-dominant analogue of howieite. It is dark brown to black ni color, luster vitreous. Streak brown. Good (010) and fair (100) cleavages. Mohs’ hardness of the aggregate is 5–6. Specific gravity 3.30 (meas.), density 3.34 (calc. on unit cell data) and 3.31 (calc. on Gladstone-Dale’s law). It is optically biaxial, negative, 2V about 70°, refractive indices α=1.697, β=1.720, γ=1.732. Pleochroism and absorption are X=pale golden yellow, Y=yellowish brown, Z=dark brown; X<Y<Z. Infrared spectrum shows strong absorptions at 3525, 3420, 1029, 969, 617, 478 and 430 cm⁻¹. These properties indicate a close relation of the mineral to howieite. The mineral occurs as aggregates of needle-like crystals in cracks or as subordinate component in metamorphosed ferruginous chert belonging to glaucophane schist facies at the Taneyama mine, Kumamoto Prefecture, Southwestern Japan.

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Structure variation with octahedral cation substitution in manganoan germanate micas KMg_3−xMn_xGe₃AlO₁₀F₂ has been examined by refining the structures of two specimens with Mg/Mn ratios of about 1/0.3 and 1/2. The crystals are monoclinic with the space group C2⁄m. The cell dimensions are a=5.435(1), b=9.413(2), c=10.458(3) Å and β=100.03(3)° in the Mg-rich specimen and a=5.489(1), b=9.509(1), c=10.462(3) Å and β=100.12(2)° in the Mn-rich one. The stuctures were refined with the full-matrix least-squares procedure to the final R values of 0.039 for 1528 observed reflection data of the Mg-rich specimen and 0.050 for 1413 reflection data of the other. The mean Ge,Al-O distance in (Ge,Al)O₄ tetrahedra is 1.746 Å in the former specimen, while 1.749 Å in the latter. Octahedral cations are randomly distributed over the two independent octahedral sites in each specimen. The tetrahedral rotation angles are 14.9° and 13.2° in the Mg-rich and Mn-rich ones, respectively. The thickness of the octahedral sheet increases approximately linearly with the degree of octahedral substitution and that of the tetrahedral sheet remains almost constant, while the interlayer thickness shows a discontinuous change.

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