Abū ʿAbd Allāh Muḥammad ibn ʿAbd Allāh al-Manṣūr (Arabic: أبو عبد الله محمد بن عبد الله المنصور; 744 or 745 – 785), known also by his regnal name Al-Mahdī (المهدي, "He who is guided by God"), was the third Abbasid Caliph who reigned from 775 to his death in 785. He succeeded his father, al-Mansur.
 
This gold dinar struck in year AH 161 (AD 778/779) graded mint state MS-62 by NGC. 
 
No mint (likely Madinat al-Salam)
 
4.23 grams of highly refined gold.  Meant to compete in world trade with the Eastern Roman Empire solidus.  Much Luster.  No problems.  Well centered.
 
Usually these coins are dull, encrusted, worn, scratched, bent, filed, clipped, cleaned improperly, marred by graffiti and camel hairlines, sandblasted, or, you guessed it, Persian rug burned.