单晶
The opposite of a single crystal is an amorphous structure where the atomic position is limited to short range order only. In between the two extremes exist "polycrystalline", which is made up of a number of smaller crystals known as "crystallites", and "paracrystalline" phases. Single crystals will usually have distinctive plane faces and some symmetry, where the angles between the faces will dictate its ideal shape. Gemstones are often single crystals artificially cut along crystallographic planes to take advantage of refractive and reflective properties.