Amchoor (amchur) powder is also referred to as "mango" powder. It is made from green dried, ground mangoes. In Hindi, the word aam means mango and choor is powder. The spice imparts a tart and slightly sour flavor to many Indian dishes including fish, meats, vegetables and curries. It can also be used as a meat tenderizer and even as part of a coating for fish.
Amchoor tends to get lumpy so you should always crumble it to remove the lumps before you use it.
Purchase amchoor in any Indian market and some Asian grocery stores. Or, buy amchur online at Amazon.com Amchur (Dry Mango) Powder 3.5oz
If you don't have amchoor you can substitute: