Identify the figure of speech used in this sentence
He had a heart of stone.
The figure of speech used in the sentence "He had a heart of stone" is metaphor.
Complete the following task based on the instruction and optional input provided.### Instruction:
Identify the figure of speech used in this sentence

### Input:
He had a heart of stone.

### Output:
The figure of speech used in the sentence "He had a heart of stone" is metaphor.