Twinnings

Twinnings denotes multiple instances or examples of twinning, a term used in several fields to describe the formation of a twin or pair, or to partnerships created between communities. The most common senses are in urban diplomacy and crystallography.

In urban diplomacy, town twinning or sister city relationships link municipalities to promote cultural exchange, educational projects, and economic ties. These twinnings often involve formal agreements, exchange visits, joint cultural events, and the sharing of best practices. They are typically guided by twinning committees or networks and may be supported by national or regional authorities.

In crystallography, twinning occurs when two or more crystal domains of the same mineral grow together in a symmetrical relation. Twin boundaries can influence mechanical and optical properties of the material. Common twinning modes include contact twinning, penetration twinning, and rotation twinning, each described by a twin law and a specific orientation relationship. The plural term “twinnings” refers to multiple twin domains within a single specimen or to multiple instances of twinning observed in different samples.

Other uses are rare; outside these contexts, the term is typically replaced with more precise language. In everyday language, twinning is usually discussed in its singular form, with twinnings reserved for describing collections of twinning instances or relationships.