Calcium carbonate is just limestone or marble dust (used in plaster) -- it's not something you add to your pool. Rather it forms when you have excess carbonate ions (from sodium carbonate or bicarbonate), calcium ions (from calcium chloride flake or beads, calcium hypochlorite . . . or your pool's walls), all at a high-ish pH level.

Probably, you are thinking of calcium chloride. The dihydrate (77% calcium chloride) is a flake; the anhydrous (90+%) is usually beads. The dihydrate (chemically bound water) is far more commonly sold than the anhydrous (no water) material).