Cleavage - cleavage

Japanese: へき開(劈開) - へきかい（英語表記）cleavage

[Crystal cleavage]
When mechanical force is applied to a crystal, it may break along a specific crystallographic plane, resulting in the appearance of a smooth surface. This phenomenon is called cleavage, and the surface that appears is called a cleavage plane. This is a brittle fracture, and crystals that are prone to cleavage are fragile. The cleavage plane is determined by the arrangement of the atoms that make up the crystal, and the plane with the highest atomic density is usually the cleavage plane. Crystals with the same crystal structure also have the same cleavage plane. The degree of cleavage ranges from complete and clear, such as in mica, graphite, and calcite, to almost no cleavage, such as in quartz and garnet.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

［結晶のへき開］
　結晶に機械的な力を加えると特定の結晶学的な面に沿って割れ，平滑な面が出現することがある。この現象をへき開といい，出現した面をへき開面と呼ぶ。これは脆性（ぜいせい）破壊であり，へき開しやすい結晶はもろい。へき開面は結晶を構成する原子の配列で規定されていて，原子密度が高い面が通常へき開面となる。結晶構造が同一である結晶間では，へき開面も同じ結晶面となる。へき開の程度には雲母や石墨や方解石のように，完全で明瞭なものから，水晶やザクロ石のように，ほとんどへき開しないものまである。

出典　株式会社平凡社世界大百科事典第２版について　情報

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