A trioctahedral member of the true mica group. The end-member formula is KLiMn³⁺₂Si₄O₁₂. The chemical composition of norrishite is noteworthy because it is Li- and Mn-rich and anhydrous, oxygen-rich, and fluorine-poor content. Norrishite forms as the 1M polytype (space group C2/m), and the octahedral sites show Jahn-Teller distortions (Tyrna and Guggenheim, 1991). Norrishite occurs at the (now-filled) Hoskins manganese mine, near Grenfell, New South Wales, Australia.

Nsutite was originally described as one in a series of similar manganese oxide phases called “gamma MnO₂“. Zwicker et al. (1962) showed that the samples they studied have a chemical formula more typical of a hydrous component, e.g., Mn(O,OH)₂. S. Turner (1982), in a PhD. thesis (Arizona State University), as described in Post (1999), showed that the samples he studied are comprised of random intergrowths of pyrolusite (MnO₂) and ramsdellite (MnO₂) or a ramsdellite-like phase and, therefore, classification of nsutite as a mineral is questionable. Samples have numerous structural defects and grains commonly have crystallite boundaries. Large deposits occur near Nsuta, Ghana; it has been noted in marine nodules and as residual oxidation products of Mn-rich carbonates.
Cf., vernadite

An obsolete term for muscovite.

The ratio of the major principal effective stress to the minor principal effective stress among three orthogonal planes at any stressed point, where there are zero shear stresses.

Inappropriate usage for an octahedral sheet.
See octahedral sheet

For phyllosilicates, an octahedral sheet contains edge-sharing octahedra that are connected in a continuous two-dimensional arrangement. These octahedra generally contain small (e.g., Al, Fe³⁺) or medium size (e.g., Mg, Fe²⁺, Li) cations with coordination anions (e.g., O, OH, Cl, S). In some phyllosilicates (e.g., modulated phyllosilicates), the octahedral sheet may be only partially continuous, for example, forming one-dimensional strips of octahedra or islands of octahedra. There are two types of octahedral sheets, dioctahedral and trioctahedral. After Guggenheim et al. (2006) and references therein.
Cf., dioctahedral sheet, trioctahedral sheet, plane, layer

An obsolete term for biotite.

An obsolete term for biotite.

A Fe₊₃-rich, green, 1:1 serpentine type clay mineral that is intermediate between dioctahedral and trioctahedral, approximately (Fe³⁺, Fe²⁺, Mg, Al, Ti, Mn²⁺)_2.5(Si,Al)₂O₅(OH)₄. Odinite forms primarily as 1M (space group Cm) with lesser amounts of 1T (trigonal or hexagonal) polytypes. Octahedral cation totals range from 2.30 to 2.54 cations per 3.0 sites for samples described. Apparently forms in association with organic material on shallow marine shelves and reef lagoonal areas in tropical latitudes.

An obsolete term for biotite.