石井 仁司（津田塾大学・研究員／早稲田大学・名誉教授）

講演題目

ダイヤモンドの双子再訪

Diamond twin revisited

英文サマリ

As noticed in 2006 by the speaker of the present talk, the hypothetical crystal---described by crystallographer F. Laves (1932) for the first time and designated "Laves' graph of girth ten" by geometer H. S. M. Coxeter (1955)---is a unique crystal net with a remarkable symmetric structure similar to the diamond crystal, thus deserving to be called the diamond twin although their shapes look quite a bit different at first sight. In this talk, I shall observe an interesting mutual relationship between them, expressed in terms of "orthogonally symmetric lattice," a generalization of irreducible root lattices. This may give further justification to use the word "twin."