A natural solid with insufficient long-range atomic ordering to be classified as a mineral. For example, limonite (FeO . OH . nH2O) is often considered an amorphous “mineral” or mineraloid.
A natural solid with insufficient long-range atomic ordering to be classified as a mineral. For example, limonite (FeO . OH . nH2O) is often considered an amorphous “mineral” or mineraloid.
A poorly defined material, possibly interstratified biotite and vermiculite.
A modulated 2:1 layer silicate with a continuous octahedral sheet and a tetrahedral sheet that forms linked hexagonal 6-fold tetrahedral rings along strips along the [010] direction (Guggenheim and Eggleton, 1986). Some of the tetrahedra are partially inverted to form a chain along the [010], and this chain links adjacent 2:1 layers. There are two varieties of minnesotaite that are based on strip widths and chemical composition: a P cell is Mg-rich and is formed where 10 tetrahedra span 9 octahedra along the [010] whereas a C cell, which is Fe-rich, forms with 9 tetrahedra spanning 8 octahedra. The ideal chemical composition for the P cell is (Fe,Mg)30Si40O96(OH)28 and (Fe,Mg)27Si26O86(OH)26 for the C cell. Early workers incorrectly considered minnesotaite as the Fe analogue of talc. Minnesotaite occurs in low grade metamorphic silicate iron formations.
Or symmetry plane, used to describe a repetition of features whereby identical points occur an equal but opposite distance along any line perpendicular from this imaginary plane. Consequently, an object is “bilateral” in that it shows a matching of features (also referred to as “reflection”) but a change in “handedness”, e.g., most people, standing with arms by their sides and feet side-by-side, have a mirror (bilateral or reflection) relationship between the left side and the right side.
Cf., symmetry, center of symmetry, rotation symmetry
An obsolete term.
See Southern bentonite.
An obsolete term.
See Southern bentonite.
See suspension.
See interstratification.
A Fe-,Mg-rich chlorite, heat treated in air for one-hour at 550oC to produce a chlorite-like structure (Guggenheim and Zhan, 1999) with a strong d(001) peak (14 Å) and weak or absent higher order 00l peaks. The chlorite-to-modified chlorite reaction allows the identification of mixtures of 7 Å phases (e.g., kaolin minerals) and Fe-,Mg-rich chlorite after heating samples of clay mixtures that may contain chlorite with moderate to high amounts of Fe by revealing the possible presence of 7Å peaks in an oriented clay mineral aggregate.
A polymorph of quartz, has lower symmetry than quartz (I2/a) and a triclinic superstructure commonly occurs. The structure was described by Miehe and Graetsch (1992) as comprised of sections of right- and left-handed quartz alternating at the unit cell level to form a framework of corner sharing tetrahedra. The framework has 4-, 6- and 8-fold rings, and there is no open tunnel as found in alpha quartz. The nanoscale alternation follows the Brazil twin law, but because it is periodic at the unit cell level, moganite represents a (metastable) mineral phase. Moganite occurs as intergrowths with (alpha) quartz in chert, quartzine, flint, and chalcedony, thus indicating that these latter varieties are not minerals, but rock names. Any H2O present in moganite is not structurally required.