Cristobalite is a mineral polymorph of silica, formed at high-temperatures. It is used in dentistry as a component of alginate impression materials as well as for making models of teeth It has the same chemical formula as quartz, SiO2, but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all the members of the quartz group, which include coesite and stishovite. Cristobalite occurs as white octahedra or spherulites in acidic volcanic rocks and in converted diatomaceous deposits in the Monterey Formation of the US state of California and similar areas. Cristobalite is stable only above 1470 °C, but can crystallize and persist metastably at lower temperatures, it is named after Cerro San Cristóbal in Pachuca Municipality, Mexico. The persistence of cristobalite outside its thermodynamic stability range occurs because the transition from cristobalite to quartz or tridymite is "reconstructive", requiring the breaking up and reforming of the silica framework; these frameworks are composed of SiO4 tetrahedra in which every oxygen atom is shared with a neighbouring tetrahedron, so that the chemical formula of silica is SiO2.

The breaking of these bonds required to convert cristobalite to tridymite and quartz requires considerable activation energy and may not happen on a human time frame. Framework silicates are known as tectosilicates. There is more than one form of the cristobalite framework. At high temperatures, the structure is Fd3m, No. 227, Pearson symbol cF104. A tetragonal form of cristobalite occurs on cooling below about 250 °C at ambient pressure and is related to the cubic form by a static tilting of the silica tetrahedra in the framework; this transition is variously called the low-high or α − β transition. It may be termed "displacive". Under rare circumstances the cubic form may be preserved if the crystal grain is pinned in a matrix that does not allow for the considerable spontaneous strain, involved in the transition, which causes a change in shape of the crystal; this transition is discontinuous. The exact transition temperature depends on the crystallinity of the cristobalite sample, which itself depends on factors such as how long it has been annealed at a particular temperature.

The cubic β phase consists of dynamically disordered silica tetrahedra. The tetrahedra remain regular and are displaced from their ideal static orientations due to the action of a class of low-frequency phonons called rigid unit modes, it is the "freezing" of one of these rigid unit modes, the soft mode for the α–β transition. In the α–β phase transition only one of the three degenerate cubic crystallographic axes retains a fourfold rotational axis in the tetragonal form; the choice of axis is arbitrary. These different twin orientations coupled with the discontinuous nature of the transition can cause considerable mechanical damage to materials in which cristobalite is present and that pass through the transition temperature, such as refractory bricks; when devitrifying silica, cristobalite is the first phase to form when well outside its thermodynamic stability range. This is an example of Ostwald's step rule; the dynamically disordered nature of the β-phase is responsible for the low enthalpy of fusion of silica.

The micrometre-scale spheres that make up precious opal exhibit some x-ray diffraction patterns that are similar to that of cristobalite, but lack any long-range order so they are not considered true cristobalite. In addition, the presence of structural water in opal makes it doubtful that opal consists of cristobalite. American Geological Institute Dictionary of Geological Terms. Durham, D. L. "Monterey Formation: Diagenesis". in: Uranium in the Monterey Formation of California. US Geological Survey Bulletin 1581-A, 1987. Reviews in Mineralogy and Geochemistry, vol. 29. Silica: behavior and physical applications. Mineralogical Society of America, 1994. R. B. Sosman, The Phases of Silica. International Chemical Safety Card 0809

Attack Force (film)

Attack Force is a 2006 American science fiction thriller action film directed by Michael Keusch, written and produced by Steven Seagal, who stars in the film. The film co-stars David Kennedy; the film was released on direct-to-DVD in the United States on December 5, 2006. Marshall Lawson is the commander of an elite U. S. military unit. During an overseas assignment in Paris, Lawson loses all three of his men in a random attack on their hotel room, he takes it upon himself to investigate the attack, with the help of his girlfriend Tia and his friend Dwayne. Marshall uncovers CTX, a covert military drug so secret that an arm of the military headed by a man named Werner wants Marshall eliminated. Tia turns out to be one of the two military scientists who developed CTX. Reina, the hooker who slaughtered Marshall's team, was under the influence of CTX; the drug gives its users superhuman strength and agility, but irrevocably drives them to violence. The other co-inventor of CTX is Aroon, now a Paris night club owner.

Aroon has plans to release the CTX into the Paris' water supply, which would turn the city's residents into deranged killers. Marshall and Dwayne must stop Aroon and Werner before that happens. Steven Seagal as Marshall Lawson Lisa Lovbrand as Tia David Kennedy as Dwayne Danny Webb as Werner Gabi Burlacu as Tia's agent Matthew Chambers as Seth Vlad Coada as Tia's Agent #3 Adam Croasdell as Aroon Mark Dymond as Phil Florian Ghimpu as Tourist Vlad Iacob as Tia's Agent Ileana Lazariuc as Queen Sayed Najem as Hitman Guard Daniel Pisica as Lead Team Soldier Filming took place at Castel Film Studios in Bucharest, Romania from January 7 to March 8, 2006; when the film was first announced under the name Harvester, the plot description described a different scenario than the one in the finished film. In an email exchange between Seagalogy author Vern and co-writer Joe Halpin prior to the release of Attack Force, Halpin confirmed that although the movie had been written with a sci-fi element, it had been shot in two ways: one explained the villain's actions as the work of European mobsters, the other explained them as the work of aliens.

Asked if the alien plot elements would be present in the final cut, Halpin answered "Who knows," explaining that the producers and Seagal would come to an agreement in post-production. In the finished film, the villains are explained to be gangsters, no reference is made to any extraterrestrial origin. Critics and fans have speculated that leaving the nature of the story unresolved during principal photography led to the pervasive use of other actors overdubbing dialogue that occurs in the finished film. Seagal's 2005 film Submerged appears to have undergone a similar post-production process; the film was not well received. David Nusair of Reel Film Reviews called it, "flat-out unwatchable," and "egregiously shoddy," claiming, "even the most ardent Seagal fan would be hard-pressed to sit through this monstrosity of a production in just one sitting." Seagalogy author Vern noted " does a bare minimum, the lowest amount he can get away with and still seem like the star. Not much fighting, not always appearing in his own scenes, no speeches," but goes on to note, "...

I don’t agree that it’s his worst," comparing it favorably to Seagal's previous film, 2006's Shadow Man. Several reviewers complained about the perceived slapdash nature of the film, in particular the extensive use of an obvious voice double overdubbing much of the dialogue from Seagal. Attack Force on IMDb Attack Force at AllMovie Attack Force at the TCM Movie Database

Rough Romance

Rough Romance is a 1930 American adventure film western directed by A. F. Erickson; the film stars George O'Brien, Helen Chandler, Antonio Moreno, Roy Stewart, Harry Cording and a 23-year-old John Wayne had a minor uncredited role. Working as lumberjacks in the Northwestern United States, Billy West and his pal Laramie spy two men stealing furs from a trap, but they arrive too late to save the trap owner from being shot. Billy suspects his partner Chick Carson. While Marna Reynolds dreams of dances and pick chiffon dresses, her father is being forced to purchase stolen furs from LaTour and Carson, LaTour is throwing a few lecherous glances toward Marna. Billy, in a card game, catches LaTour cheating and suggests he suspects him of theft and murder before further violence is stopped by the sheriff. Billy and Laramie are ambushed and Billy is shot in the shoulder, but kills Carson. Laramie takes Billy to the Reynolds trading post. LaTour convinces the sheriff that Billy murdered Carson and the sheriff is led on a dogsled chase by Laramie.

LaTour returns to the post with intentions of changing his lecherous glances into lecherous action, the weakened Billy struggles with LaTour as Marna races toward the log-jammed river. George O'Brien as Billy West Helen Chandler as Marna Reynolds Antonio Moreno as Loup La Tour Roy Stewart as Sheriff Milt Powers Harry Cording as Chick Carson David Hartford as "Dad" Reynolds Noel Francis as Flossie Frank Lanning as Pop Nichols John Wayne as Lumberjack While Wayne had a bit part in this film and worked on props, he was not given a props credit as shown by some sources. If he had been, he would have been the first and only props worker given an on-film credit in 1930. John Wayne filmography Rough Romance on IMDb