From Glossary of Meteorology
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 plane), 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.
Copyright 2022 American Meteorological Society (AMS). For permission to reuse any portion of this work, please contact firstname.lastname@example.org. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act (17 U.S. Code § 107) or that satisfies the conditions specified in Section 108 of the U.S.Copyright Act (17 USC § 108) does not require AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a website or in a searchable database, or other uses of this material, except as exempted by the above statement, require written permission or a license from AMS. Additional details are provided in the AMS Copyright Policy statement.