Vanadium pentoxide - V2O5
Vanadium pentoxide can be obtained in all kinds of purities. This sample was obtained from a ceramics and pottery supplier and I was fortunate to have received such a pure sample.
Pure vanadium pentoxide has a bright yellow/brown/orange color. When the material is impure, then it is dirty brown/grey. The material received from ceramics shops has a very variable composition. One batch can be very pure (over 99.5% purity can be obtained), while other batches are quite impure and contain several percents of ammonium metavanadate. For experiments with vanadium, the presence of the ammonium metavanadate, however is not of a real concern.