WILLIAM SHAKESPEARE: Twelfth Night
Read the extract below and answer the question
I have said too much unto a heart of stone,
And laid my honour too unchary on 't;
There's something in me that reproves my fault,
But such a headstrong potent fault it is
That it but mocks reproof.
(Acts iii, Scene 4)
The figure of speech used in '' a heart of stone'' is