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Actually its correct name is SHYAH JEERA instead of Shah Jeera. Shyah means black. So shyah jeera use to be black in colour and having very good fragrance in it. Fragrance use to be different from simple JEERA but its called jeera because its looks like the normal jeera.
Shyah jeera used in biryaani and some other mughlai dishes for taste and fragrance.