Structural relationships between β-gallia, rutile, hollandite, psilomelane, ramsdellite and gallium titanate type structures

Abstract

The relationships between the above structure types are considered theoretically. New types of tunnel structures and transformation mechanisms are derived. The analysis predicts many variations of the hollandite structure type previously unsuspected. These go some way towards explaining the indefinite structural results obtained using X-ray diffraction techniques for hollandite and related minerals and also for ),-manganese oxides and hydroxides. It is strongly suggested that preparative and characterization techniques need to be far more thorough and penetrating than those used so far, if significant measurements of physical properties, such as superionic conductivity, are to be made.

Crystal chemistry of six-coordinated silicon: a key to understanding the earth's deep interior

“…edge-sharing octahedral chains of rutile; the double chains of hollandite; the corner-sharing octahedral sheets of perovskite; the face-sharing topology ofilmenite) that can link together in many ways to form ordered superstructures of great complexity. Such complexity was recognized by Wadsley (1964) and Bursill (1979) in their descriptions of modular rutile-hollandite-flGa203 structures, and it is realized in the homologous series including phase B, anhydrous phase B and several other structures. Phase B, for example, is based on oxygen close packing, yet it has 40 independent atoms in its asymmetric unit to yield one of the most complex ternary silicates yet described.…”

“…Bursill (1979) extended his discussion to a number of more-complex structures that combine the MX2 forms described above with fl-Ga203 topology, which is based on the same type of double edge-shared chains as found in hollandite. A range of gallium titanates, such as Ga4TiOs, Ga4Ti7020 and Ga4Ti21048 (all members of the homologous series Ga4Ti,"_4-O2,1 2 that couple rutile and "),-Ga203 units) are illustrated, as are ternary Ba-Ga-Ti oxides that unite components of rutile, hollandite and ),-Ga203.…”

“…All seven high-pressure [V~Jsi structures without tetrahedral Si are isomorphs of room-pressure oxides with trivalent or tetravalent transition metals (Ti, Mn or Fe) in octahedral coordination. Bursill (1979). Rutile has single chains, leading to 1 x 1 square channels, while hollandite and calcium ferrite have double chains, yielding larger channels.…”

Metalogenia del depósito de manganeso Santa Rosa, Baja California Sur, México

“…La romanechita presenta una estructura cristalina semejante a la de la holandita BaMn 8 O 16 y la todorokita (Mn, Mg, Ca, Ba, K, Na) 2 Mn 3 O 12 ·3H 2 O (Bursill, 1979;Turner y Buseck, 198l;Vasconcelos, 1999). La estructura de la romanechita está construida por cadenas dobles y triples con octaedros de MnO 6 con borde compartido que se une para formar grandes túneles con secciones cruzadas rectangulares, de dos por tres octaedros (Post, 1999 (Turner y Post, 1988;Vasconcelos, 1999); las cargas de los cationes del túnel están balanceados por substitución de Mn(III) por Mn(IV).…”

“…Debido a su estructura interna la romanechita puede tener cantidades variables de Ba y H 2 O, por su relación de reemplazamiento isomórfico, en proporciones generalmente 1:2, respectivamente (Wadsley, 1953;Bursill, 1979; Figura 9. Histogramas mostrando la distribución de la temperatura de fusión del hielo (Tfh ºC) y temperatura de homogenización (Th ºC), para inclusiones analizadas en cristales de barita de Santa Rosa, de las etapas de mineralización de veta-brecha y brecha.…”