[Sca-cooks] OOP: Mystery flour-like substance in my cabinet

[Pixel, Goddess and Queen]

Usually I remember to label the various canisters and bottles and things 
in my cabinets, unfortunately I seem to have neglected one. I have a 
canister of some substance, in the quantities that would suggest it came 
in a 5-pound bag, that I can't identify. It might be rice flour. It is 
very white, whiter than the unbleached white wheat flour, but I think not 
quite as white as cornstarch. It is slightly granular rather than powdery. 
Is there any good way for me to confirm that this is, indeed, rice flour?

Thanks!
Margaret Fitzwilliam