RIFQI ZAKARIA 111.130.137 CLASS DCrystalA crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. Crystallography is the scientific study of crystals and crystal formation. The word crystal is derived from the ancient Greek word (krustallos),which had the same meaning.Crystallization is the process of forming a crystalline structure from a fluid or from materials dissolved in the fluid. A noncrystalline material, which has no long-range order, is called an amorphous, vitreous, or glassy material. It is also often referred to as an amorphous solid, although there are distinct differences between solids and glasses: most notably, the process of forming a glass does not release the latent heat of fusion.Crystalline structures occur in all classes of materials, with all types of chemical bonds. Polymorphism is the ability of a solid to exist in more than one crystal form. For example, water ice is ordinarily found in the hexagonal form Ice Ih, but can also exist as the cubic Ice Ic, the rhombohedral ice II, and many other forms. Amorphous phases are also possible with the same molecule, such as amorphous ice. In this case, the phenomenon is known as polyamorphism. For pure chemical elements, polymorphism is known as allotropy. For example, diamond, graphite, and fullerenes are different allotropes of carbon. Crystalline rock masses have consolidated from aqueous solution or from molten magma. The vast majority of igneous rocks belong to this group and the degree of crystallization depends primarily on the conditions under which they solidified. Such rocks as granite, which have cooled very slowly and under great pressures, have completely crystallized, but many lavas were poured out at the surface and cooled very rapidly; in this latter group a small amount of amorphous or glassy matter is frequent. Other crystalline rocks, the evaporites such as rock salt, gypsum and some limestones have been deposited from aqueous solution, mostly owing to evaporation in arid climates. Still another group, the metamorphic rocks which includes the marbles, mica-schists and quartzites; are recrystallized, that is to say, they were at first fragmental rocks, like limestone, shale and sandstone and have never been in a molten condition nor entirely in solution. The high temperature and pressure conditions of metamorphism have acted on them erasing their original structures, and inducing recrystallization in the solid state.