noun
submetallic luster
Geological term describing a mineral's luster that is less brilliant than metallic but still reflective, like that of certain ores.
この鉱物は亜金属光沢を示す。
This mineral exhibits a submetallic luster.
金属光沢 refers to a fully metallic luster, while 亜金属光沢 is a less intense, submetallic luster.
Compound of 亜 (a, 'sub-') + 金属 (kinzoku, 'metal') + 光沢 (kōtaku, 'luster'). A straightforward technical term.