A more or less regular periodic array of atoms, molecules, or ions, usually forming a solid. In everyday parlance crystal is used in a bewildering variety of ways, sometimes contradictory. Fine glassw
are is called crystal, although glass, an amorphous solid, is the antithesis of a crystal. A solid with facets exhibiting external symmetry may be called a crystal, although a solid without such facets may still be a crystal. A pure liquid such as water is said to be crystal clear even though transparency is not an essential property of a crystal.
A solid body whose atoms or molecules have a regularly repeated arrangement called crystal lattice. The latter may be outwardly expressed by plane faces (see crystal facet). Single crystals grow from
a single nucleus (see also grain). Skeleton type or hopper crystals grow faster along their edges than in the centres of their faces, so that the faces appear to be recessed. This type of skeletal recrystallization usually determines the morphology of depth hoar crystals.
Usually dark metallic or plastic screen that simplifies snow crystal analysis by providing a grid to determine grain shape and size. Also known as crystal screen.
A crystal face, i.e., a small, plane or flat surface of a crystal. Facets appear on many growing crystals because some surfaces grow much more slowly than others.
Any characteristic external crystalline form. For an ice crystal, may refer just to the ratio of the lengths of the crystal parallel to its c and a axes (at 90 to or parallel to the hexagonal basal pl
ane), but usually it simply means the crystal shape, including dendritic, skeletal, prismatic, sectors, etc. The term is not applied to the internal crystal lattice. Slight variations in the growth rates of different crystal planes in a given crystal structure lead to quite different crystal habits. Such growth rate variations may result from variations in temperature and water vapor supersaturation of the environment in which the crystal grows.
Hoarfrost that exhibits a relatively simple macroscopic crystalline structure; to be distinguished from amorphous frost. Crystalline frosts are classified into five forms: 1) needle; 2) featherlike; 3
) plate; 4) cup; and 5) dendritic. Such ice forms are typically developed as a result of deposition at temperatures well below 0C, the degree of supersaturation and temperature controlling the form.
Crystallization is the (natural or artificial) process of formation of solid crystals precipitating from a solution, melt or more rarely deposited directly from a gas. [Wikipedia]
The process of formation of a crystal (an ordered state) from a disordered (gas) or partially ordered (liquid) state. Examples are the freezing of liquid water, the deposition of water vapor (frost),
and crystal formation in supersaturated solutions.