[Question] What would cause a pork shoulder bone to crumble like chalk and be dark inside after being cooked in a crock pot?

I've been doing a keto diet this year and eating a lot of meat. I've literally cooked dozens of pork shoulders (9-11 lbs) over the last 7 months. Usually on high for 12-16 hours.My last one however turned out different. After it's cooked, I usually cut off the fat, take out the bone, and shredded the meat. The fat and bone usually go to my brother's dog. This time however when I used tongs to grab the bone it crumbled like chalk. Took me a sec to realize what happened. Tried again and it broke to pieces again. I eventually split the meat and took the bone out and was able to poke a knife it it. Inside was a dark mush, sort of like coffee grounds. I've never seen a bone do that and don't know why this one turned out differently . Anyone have any experience like this or guesses? via /r/food http://ift.tt/2uqWohe