Ice crystal

An ice crystal is solid water whose molecules occupy an ordered lattice, most commonly with hexagonal symmetry. Its growth conditions shape its form, from plates and columns to branching snowflakes.

Hydrogen bond: An attraction between a hydrogen atom bonded to an electronegative atom and another electronegative atom. Hydrogen bonds connect water molecules into the lattice that gives ordinary ice its structure.
Water molecule: A molecule consisting of two hydrogen atoms bonded to one oxygen atom. Its bent shape and polarity enable the directional attractions that organize ice.
Snow: Precipitation composed of ice crystals, usually joined into flakes or aggregates. Falling ice crystals and their aggregates make snow and build snow cover.
Amorphous ice: Solid water lacking the long-range molecular order characteristic of crystalline ice. It is frozen water without the repeating lattice that defines an ice crystal.
Ice Ih: The common hexagonal crystalline phase of ice found naturally on Earth. Most atmospheric ice crystals and familiar frozen water have this lattice structure.
Crystal lattice: A repeating arrangement of points that represents the ordered structure of a crystal. The lattice is the repeating spatial pattern occupied by molecules in crystalline ice.
Cirrus cloud: A high-altitude cloud composed mainly of ice crystals, appearing as thin filaments or patches. Its appearance and radiative effects depend on the shape and distribution of airborne ice crystals.
Ice Ic: A metastable cubic crystalline phase of ice with a structure related to diamond. Its cubic symmetry contrasts with the hexagonal symmetry of ordinary atmospheric ice.
Ice nucleation: The formation of an initial stable ice structure from supercooled water or vapor. Crystal growth begins when nucleation creates a stable seed.
Phase transition: A transformation between distinct physical states of matter or phases of a material. Freezing changes liquid water into an ordered solid phase.

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