As an adjective:
* Despite the evidence against him, the defendant remained adamant in his claim of innocence.
* The teacher was adamant that all students complete their homework by Friday.
* She was adamant about her decision to quit her job, no matter how much her friends tried to persuade her otherwise.
As a noun (less common):
* Her refusal to budge was an adamant wall against his pleas.
* The general's adamant stood strong against the enemy's attack. (This usage is more poetic and emphasizes the strength of the person's resolve)
Remember, "adamant" usually describes someone who is stubborn or unyielding in their belief or decision.