From my studies most fatwood occurs when a pine tree dies in an upright position. The resin settles to the lower areas and gets really concentrated. Over time the upper and outer areas weather away leaving the area super concentrated with pitch behind because it won't absorb water and won't rot. The best fatwood I find is in old root sections under ground with barely any above ground signs of the tree that once stood there. The good stuff will smell very strongly or turpentine, be very glossy, take a spark easily and a flame even more easily, and will produce a lot of liquid pitch as it burns like the liquid fat rendered from roasting meats, hence (I think) the name "fatwood" in some places, "light-wood", "rich-pine", "lighter-pine", and probably a few other colloquial names in other places.