My initial impression was that this is a weathered sperm whale tooth but it is a little too small. Sperm whale teeth do vary in size but are usually about 6 inches long where as this is barely 3.5 inches. An alternative is killer whale, the size is about right. Killer whale teeth very in one important detail, the sharp end of the tooth is covered with hard enamel like a human tooth where as the sperm whale tooth is not. It is difficult to tell from the photo but I think that I can make out enamel on the crown of the tooth which makes it Killer Whale.