See pyroxenoid group.
See pyroxenoid group.
See point of zero charge.
A calculation of atomic or molecular properties of a model system based on first principles (ab initio) quantum mechanics. Because quantum calculations involve either the solution or approximation of the Schrodinger equation to determine the electronic structure, this is the highest level of theory that can be used to calculate molecular-scale properties of a model system.
Cf., density functional theory
Quartz, SiO2, is comprised of two chains, both spirals of SiO4 tetrahedra parallel to the c axis. In the alpha-quartz structure (low temperature form to 573 oC at 1 bar), these chains are kinked and the structure has trigonal symmetry. In the beta-quartz structure (high temperature form, above 574.3 oC), the chains expand (the tetrahedra are not twisted) and the symmetry is hexagonal with a more open structure than the alpha form. The beta form is non-quenchable and not found under ambient conditions. An intermediate phase between 573 – 574.3 oC is known to exist. Quartz is a common associated phase in clay, but generally forms grains larger than clay particles (about 0.2 – 0.4 micrometers) and therefore quartz particles can be removed by size separation.
Quartz, SiO2, is comprised of two chains, both spirals of SiO4 tetrahedra parallel to the c axis. In the alpha-quartz structure (low temperature form to 573 oC at 1 bar), these chains are kinked and the structure has trigonal symmetry. In the beta-quartz structure (high temperature form, above 574.3 oC), the chains expand (the tetrahedra are not twisted) and the symmetry is hexagonal with a more open structure than the alpha form. The beta form is non-quenchable and not found under ambient conditions. An intermediate phase between 573 – 574.3 oC is known to exist. Quartz is a common associated phase in clay, but generally forms grains larger than clay particles (about 0.2 – 0.4 micrometers) and therefore quartz particles can be removed by size separation.
Quartzine is a rock term to describe a mixture of a fibrous [0001] variety of microcrystalline (length slow) quartz and moganite. Cf., chalcedony
Quartzine is a rock term to describe a mixture of a fibrous [0001] variety of microcrystalline (length slow) quartz and moganite.
Cf., chalcedony
In micromorphology of soils, quasi-coating is a pedofeature that consists of a layer of material related to surfaces (i.e., voids, grains, aggregates) but not immediately adjacent to the surface.
Syn., quasi-cutan.
Cf., hypo-coating
See quasi-coating.
Alkylammonium salts, such as hexadecyltrimethylammonium bromide, have four alkyl or methyl groups attached to nitrogen with a permanent positive charge. The similar n-hexadecylamine hydrochloride used in the alkylammonium layer charge method is only positively charged in neutral to acidic solutions.
See alkylammonium layer charge method