Maybe 3 or 4 basement ceiling joists, out of dozens, had this oddness. At first I thought it was termite damage, but closer examination seems like it might be old, crystalized sap pockets? (A complete guess). Pockets are only about a 1/4" thick inside the joists.
Probed joists open and this stuff fell-out (third pict). Rigid flakes that could be crushed into a powder with your fingers. If you look closely at the first picture, there is another horizontal crack along the top of the joist parallel to the visible bottom crack, and it almost looks like the *stuff* in the joist expanded and pushed-out the face of the joist to cause the cracking. Never seen anything like it, and nothing like termite damage or powder post beetle damage I've ever seen. Not widespread either. Rest of each subject joist is solid.
Does anyone know what this is?