Silicon dioxide surrounds us on all sides. The soil we walk on contains silicon dioxide sand. The windows that decorate our houses and public buildings are made of silicon dioxide glass
Several different crystalline forms of silicon dioxide occur in nature. We refer to each of these crystalline forms as polymorph silicon dioxide. Polymorphus is from the Greek words, which is many and form.
Vicus
Quartz is the most common form of crystalline silicon dioxide. In the field, silicon and oxygen atoms bond to the lattice. Its basic unit is the tetrahedron, in which four oxygen atoms are symmetrically joined to one silicon atom. And each atom of oxygen is a constituent part of two different tetrahedra, so that all the tetrahedra are joined to form a unit.
The standard chemical formula of street is SiO2; but as you can see from the premises, the village is not composed of discrete units. It is a big molecule.
Ideally, the crystal should form a very neat hexagonal crystal with a six-sided cone at two opposite ends. But natural grass presents imperfections. This is partly due to the fact that the bonds between atoms in the crystal lattice inevitably bend at room temperature. In addition, the normal growth of the crystal can be hindered by surrounding factors, and impurities intrude into the composition of the crystal. As a result, quartz crystals are jagged and irregular. Sometimes they look like a statue, which the sculptor left half-finished;
There are two different polymorphs of wheat: alpha wheat and beta wheat. Beta-quartz is stable at higher temperatures. When it boils, the village becomes alpha. Beta-quartz crystals form better. The best alpha-vine crystals were cooled to beta-vine crystals, which managed to retain a resemblance to their original shape.
Cristobalite
Cristobalites is a polymorphic quartz that was formed at high temperatures. It was found in Cerro San Cristobal, a hill in the state of Hidalgo, Mexico.
Cristobalite is a polymorph of silica that is formed mainly at very hot temperatures. For this reason it is often found in molar rock.
Like quartz, cristobalite consists of tetrahedrons connected to form lattices. But the cristobalite tetrahedrons are connected to each other in a different way than the square. At hot temperatures, the cristobalite tetrahedra sit at the corners of the cube, but the cubic arrangement is usually lost as the temperature cools.
Crystals of cristobalite are small and often microscopic. Some appear to have an octahedral shape, while others are balls called spherulites. They appear to be cristobalite spherulites that have lost some of their silica.
Tridymite
In tridymite, the basic unit is the tetrahedron. These tetrahedra are connected to form rings. The rings are connected to form plates. Finally, the sheets are tied together to complete the rails.
Come together
Coesite has the name of Loring Coes, who was the first to draw it. It was later found in Meteor Crater, Arizona.
Cohesive tetrahedra also have their basic unit. And the tetrahedrons in coesite are connected in such a way that they form small rings, and from there the rings are connected to form chains. Because of this loose structure, the cohesion is somewhat compressed.
Cohesion needs great pressure for its formation. It occurs in metamorphic rocks.
Stishovite
Sergey Stishov synthesized stishovite in the laboratory before it was found in nature. The tremendous pressure generated by meteors is enough to trigger their formation. Like Coesite, it was first discovered in nature in the Meteor Crater of Arizona.
The basic structural unit of stishovite is not the tetrahedron, but the octahedron. Stishovite crystals are small, and the octahedra are poorly formed, but the mineral is much harder and denser.
References
The Free Dictionary by Farlex: Polymorph
http://www.thefreedictionary.com/polymorph
Wikipedia: Village
http://en.wikipedia.org/wiki/Quartz
The Street Page: SiO4 Tetrahedron
http://www.quartzpage.de/gen_struct.html
Galleries: Village group of minerals
http://www.galleries.com/minerals/silicate/quartz.htm
Mineral Web: Cristobalite mineral data
http://webmineral.com/data/Cristobalite.shtml
Porches: The mineral Cristobalite
http://www.galleries.com/minerals/silicate/cristoba/cristoba.htm
Wikipedia: Come together
http://en.wikipedia.org/wiki/Coesite
Mineralogical Society of America: High Pressure Crystal Structure and Compressibility of Coesite
http://www.minsocam.org/ammin/AM66/AM66_324.pdf
Seattle Community Network: Stishovite
http://www.scn.org/~bh162/stishovite.html
Auburn: Tridymite and Cristobalite “SiO2”
http://www.auburn.edu/~hameswe/Tridy_Cristobpage.html
