Alumina refers to Al2O3 chemical composition only and the term does not imply a structure. The term commonly is used to describe a mineraloid or a glass, as in a alumina-rich glass. Thus, alumina does not specifically refer to corundum or other alumina-rich phase (e.g., boehmite, diaspore).
Cf., mineraloid
A dioctahedral member of the true mica group. The end-member formula is KAl(Mg,Fe3+)□Si4O10(OH)2, where □ = vacancy. Typical range in composition is: viR2+ / (viR2+ + viR3+) ≥ 0.25, viAl / (viAl + viFe3+) = 0.5 – 1.0, Mg / (Mg + viFe2+) > 0.5 (Rieder et al., 1998).
A surficial AlOH group (see silanol group), which is able to incorporate or dissociate protons.
See silanol grou
“In general, silicates which contain tetrahedrally coordinated aluminum are called aluminosilicates in contrast to silicates containing octahedrally coordinated aluminum for which the term aluminum silicates is used…” (Liebau, 1985, p. 13). Although this is the classic definition of aluminosilicate, many texts use the term inconsistently. For example, kyanite and andalusite, traditionally considered part of the “aluminosilicate group” with sillimanite, do not have tetrahedrally coordinated Al, although they are closely related (structurally and geologically) to each other and sillimanite. Clearly, taking the first part of definition by Liebau (1985) as the basis of the definition, the second part should not be limited to aluminum in octahedral coordination only. Phyllosillicates are generally considered aluminosilicates, because most phyllosilicates do have Al substitution for Si, but not all do (and those minerals without tetrahedral Al present, but with Al in other polyhedral coordinations are more properly referred to as “aluminum silicates”).
See aluminosilicate.
An obsolete varietal term for manganoan muscovite and manganoan illite.
Known only in the Russian literature and not an official mineral name; the accepted name is tosudite.
A (trioctahedral) platy serpentine mineral of ideal composition of Mg2Al(Si,Al)O5(OH)4. Fe2+, Mn, Cr, Ni, and vacancies may substitute for Mg and viAl in natural samples. Natural occurrences are rare and have been noted from the Saranovskoye chrome deposit, North Urals Mountains, Russia; Chester, Massachusetts, USA; Mount Sobotka, Poland; Postmasburg, South Africa; Lake Asbestos Mine, Black Lake, Quebec, Canada; and Antarctica. The Quebec occurrence involves a rodingitized granite within a serpentinized peridotite. Stacking disorder is common but, where regular layer stacking occurs, it is most often based on a distorted 2H2 layer sequence (space group C1).
Cf., kellyite, zinalsite.
An obsolete term for muscovite.
An obsolete term for tobelite.