In order to identify five-coordinated Si(Si^v) species in crystalline and amorphous silicates by NMR spectroscopy, ²⁹Si NMR chemical shifts for the clusters of Si(CH₃)₄ (TMS), Si(OH)₄, Si(OH)₅⁻ and Si(OH)₆⁻² were calculated using ab initio molecular orbital theory. The calculated shifts relative to TMS cluster were −71.7 and −179.0 ppm for Si(OH)₄ and Si(OH)₆⁻², respectively, and are in good agreement with observed shifts. The calculated shift for Si(OH)₅⁻ was −127.4 ppm, falls just between the shifts of Si(OH)₄ and Si(OH)₆⁻². The chemical shift for Si^v species in polymerized silicates is expected to appear at about −150 ppm, if the effect of polymerization is considered. Present calculation thus supports the assignment of −150 ppm peak as Si^v species, which has been found in the alkali-silicate glasses quenched from high pressures.

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A mineral inclusion, which has a composition of 16 mole % NaPx (Na₂MgSi₅O₁₂) and 84 mole % enstatite (Mg₄Si₄O₁₂), was found in a diamond specimen from the “No. 50” kimberlite pipe in the Province of Liaoning, China. This inclusion contains a significant amount of Na₂O, and part of the silicon may be six-coordinated by oxygen. It appears to have formed at a pressure of at least 16.5 GPa, on the basis of existing high-pressure experimental results, and suggests a new phase derived from the transition zone (410–670 km). Combined with previous reports on rock samples from the transition zone, our discovery of the NaPx–En inclusion supports the proposal that the transition zone is mineralogically and geochemically heterogeneous.

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Gerstleyite [Na₂Sb₈S₁₃·2H₂O] was successfully synthesized by hydrothermal method for the first time. The syntheses condition was as follows: starting material Sb₂S₃ and Na₂S·9H₂O soln. with mixing ratio of [Sb/Na]=4.0 and 8.0 (mol/mol), heating temperature 210 and 220°C, and heating time of 80 hours. The products were identified to be gerstleyite by means of X-ray powder diffraction. Space group and lattice constants were examined by a Weissenberg camera. Crystal data: monoclinic, Cm, a=9.945(2), b=23.134(3), c=7.108(1) Å, β=127.828(8)°. The lattice parameters of the synthetic gerstleyite are 0.2∼0.4% larger than those reported for natural gerstleyite [Na₂(Sb, As)₈S₁₃·2H₂O], in which about one tenth of the Sb atoms were substituted by smaller As atoms.

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Strontian hollandite (up to 3.45 wt.% SrO) is found to occur in a piemontite-bearing quartz schist of the Sanbagawa metamorphic terrain in central Shikoku, Japan. Hollandite occurs as an aggregate of fine crystals (up to 100 μ m long) associated with braunite. From the central part of the aggregate outward, its BaO, Fe₂O₃ and TiO₂ contents increase and its MnO₂, K₂O and SrO contents decrease. Chemical variation in the hollandite suggests K (Mn⁴⁺, Ti⁴⁺)⇔(Ba, Sr)Fe³⁺ substitution. Hollandite is tetragonal or pseudotetragonal, and lattice constants are a=9.90(4) Å and c=2.87(5) Å.

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