That is not a burl it is a tree canker according to one of our turning club gurus. I don't think it is worth as much as a burl. A true burl will will have individual knots and I don't see that in your picture. I had an outting one saturday at one of our members woods and we were introduced to true burls. A canker will have interesting grain pattern.
"Canker is found on maples and these are nasty. A canker appears a sunken area on the trunk or limb and oozes sap. Fungi and bacteria spread through the tissue and the canker increases in size. At the extreme, it girdles the trunk and growth above it dies."
Last edited by Bob Willing; 02-01-2012 at 11:54 PM.