noun
allotrope
Chemistry term: different structural forms of the same element (e.g., diamond and graphite for carbon).
炭素の同素体にはダイヤモンドとグラファイトがある。
Allotropes of carbon include diamond and graphite.
Compound of 同 (same) + 素 (element) + 体 (form/body), a straightforward calque from Western chemistry terminology.