1) Comet
According to the Safety Data Sheets (SDS) published by Procter & Gamble for “PGP Comet Deodorizing Cleanser with Chlorinol” and Prestige Brands for “Comet Powdered Cleanser”, Comet cleanser contains 60–100% calcium carbonate (CaCO3). (source)
2) 325cc and 275cc
Unsolved
cc likely points to calcium carbonate.
325 mesh calcium carbonate whiting shows up on a lot of pottery sites.