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
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
A quaternary organic salt based on the phosphonium (PH4+) ion. Tetramethyl phosphonium chloride is the phosphonium analog of tetramethyl ammonium chloride.
Cf., quaternary alkylammonium salt
Landslide-prone, silty-clay to clayey-silt size sediments that become liquid upon failure (shear strength <0.5 kPa). Pre-failure strength exceeds post-failure strength by 30 (minimum) to hundreds of times. Quick clay is not thixotropic; it cannot reform after failure. ‘Quick clay’ applies only to the undisturbed material. Quick clays of Scandinavia, Eastern and Western Canada, and Alaska developed in fine-grained, glacial rock flour that accumulated in marine and brackish water during Pleistocene glacial retreat (Torrance, 2012). The salt induced a flocculated microstructure that gained strength as additional sediment accumulated. The water content approximates the high-salinity liquid limit of the sediment. Quick clays in the down-glacial-flow direction from the magnetite-rich, iron-ore deposits of Quebec and Labrador gained unusually high undisturbed strengths owing to iron-oxide cementation. Isostatic uplift elevated the deposits above sea level, and an oxidized weathered crust formed. In broad, level areas, downward percolation of rain displaced the salty pore waters. In areas adjacent to uplands, artesian pressures have displaced the salt upwards to the surface drainage system. The oxidized zone is thinner where salt removal was upward than where it was downward. During salt removal, the structure and water content remained nearly unchanged, whereas the liquid limit of the sediment decreased to its low salinity value, and the liquidity index increased from about 1.0 (high salinity) to 1.2 – 4+ (low salinity). At liquidity indices >2, the thoroughly disturbed material flows like motor oil. Chemical, mineral and microstructural factors are critical to quick-clay development. The mineralogy must be dominated by “low activity minerals” (illite, chlorite, quartz, feldspars, amphiboles, iron oxides, and carbonates). Other requirements include: flocculated microstructure (salt-induced), leaching of salt (which decreases the liquid limit), and reducing conditions that inhibit the formation of swelling clays. Experiments to produce quick clay using ‘pure’ clay, such as illite, have been unsuccessful, but using dispersed material from what had once been ‘quick clay’ has succeeded. Whereas non-swelling phyllosilicates must be present, clay-sized primary minerals also appear to be necessary. A mineralogical variant is a quick clay that developed contemporaneously in marine sediment in Japan that is dominated by low-activity (<1.1), high-ferrous-iron, non-swelling clay, and volcanic ash (Torrance and Ohtsubo, 1995). However, where oxidizing conditions develop that allow conversion of the ferrous iron to ferric iron to decrease the layer charge sufficiently to produce a swelling smectite, the resultant liquid-limit increase renders the oxidized zone no longer ‘quick’. Cf., liquid limit, liquidity index, plasticity index, quick-clay landslide, shear strength, thixotropy, Udden-Wentworth scale.
A landslide in which quick clay plays an important role. They usually start with a small triggering landslide along a riverbank or terrace, but may also be triggered by human actions or earthquakes. “Flow quick-clay landslides” occur where a substantial depth (a few meters, or more) of quick clay underlies a relatively thin surface-weathered zone. Flow failures commonly occur stepwise and retrogressively over a substantial time period (minutes to more than an hour). The liquid debris carries the thin crust out of the landslide scar and along the river valley. Very little debris remains within the scar. Flows are the norm in Scandinavia and constitute about half of the quick-clay landslides in eastern North America. In “spread quick-clay landslides”, the non-quick overburden is thicker and the large chunks of crust are difficult to transport. Once failure is initiated, the failure plane advances rapidly into the quick-clay zone and, as the quick clay liquefies and starts to move, the overburden breaks into a series of slices that are oriented perpendicularly to the direction of movement. In most cases, a large proportion of the landslide debris remains within the landslide scar. Ridges of nearly intact slices alternate with zones of liquid and plastic debris to create a ribbed, horst and graben-like topography. Spread-type landslides are rapid (tens of seconds to minutes in length).
Cf., quick clay