If it is ambergris and it appears to be. It would burn because it is supposed to be flammable. It appears to match the pictures I googled, so, there is little reason to question the professional opinion you got at the NatSci museum. You can't sell it tn the US but a guy boight a kilo sor 11,000 E. type in ambergris in your browser, the wiki one will tell about it. Any other sight than wiki will allow you to look at images.