'stone-faced' originates from the combination of 'stone' and 'face', where 'stone' implies hardness or lack of emotion, and 'face' refers to one's facial expression.

'stone-faced' has been used in English to describe someone with a hard, unemotional expression, similar to a stone.

Initially, it meant 'having a face like stone', but over time it evolved into its current meaning of 'unemotional or expressionless'.