Thanks all.
Hmmm I never thought to test how easily it dissolved. I just dropped a Citrical in water and it fully dissolved in about 5 minutes. But I forgot about the similarly-shaped Now magnesium citrate. It's been sitting in water for 10 minutes like a stone with only a slight haze so I guess that's the tablet that shows up on the X-rays. (And yet my magnesium trends a bit high so I'm obviously absorbing it eventually.)
I'm trying everything to reduce my kidney stone production and thought perhaps my calcium wasn't dissolving in order to bind with the oxalates in my intestine. Guess the issue is that the calcium prefers to bind with the unabsorbed fat, allowing the oxalates to be absorbed through the intestine wall and end up in my kidneys. No getting around having to eat a low oxalate diet. Rats-a-roni.
BTW, crushed Citrate in yogurt is not too bad. It has no taste, just makes the yogurt gritty. Never the less, I was glad when my guts healed enough to let me swallow them whole. Jarrow Bone Up has a lot of extra ingredients which differ, curiously, by whether one gets the regular 6x dose or special 3x dose. But with only 1000mg of calcium per dose, I'd have to take a (pricey) double dose which would result in me taking too much of the extra ingredients.