Ammonium metavanadate, NH4VO3, a yellow crystalline solid  which dissolves in water, is the most common laboratory vanadate reagent, along with potassium metavanadate, KVO3.
The MF of this chemical isKVO3.
Sodium metavanadate is a yellow solid which is soluble in water. Its use is limited due to its hygroscopic property. Its natural forms include mineral metamunirite (anhydrous) and a dihydrate, munirite. Both are very rare, metamunirite is now known only from V- and U-bearing sandstone formations of central-western USA and munirite from Pakistan and South Africa.