Crystalline” and “Xtal” redirect here. This article is crystalline and noncrystalline materials pdf crystalline solids.
Unsourced material may be challenged and removed. The right-angles between crystal faces are due to the cubic symmetry of the atoms’ arrangement. A crystal is a solid where the atoms form a periodic arrangement. Not all solids are crystals. These have no periodic order, even microscopically. Crystals are commonly recognized by their shape, consisting of flat faces with sharp angles.
As a crystal grows, new atoms attach easily to the rougher and less stable parts of the surface, but less easily to the flat, stable surfaces. Therefore, the flat surfaces tend to grow larger and smoother, until the whole crystal surface consists of these plane surfaces. Crystals found in rocks typically range in size from a fraction of a millimetre to several centimetres across, although exceptionally large crystals are occasionally found. The same group of atoms can often solidify in many different ways. Likewise, if a substance can form crystals, it can also form polycrystals. Polymorphs, despite having the same atoms, may have wildly different properties.
For example, diamond is among the hardest substances known, while graphite is so soft that it is used as a lubricant. Crystallization is the process of forming a crystalline structure from a fluid or from materials dissolved in a fluid. Crystallization is a complex and extensively-studied field, because depending on the conditions, a single fluid can solidify into many different possible forms. Large single crystals can be created by geological processes.