Calcium carbonate is one of the most common forms of calcium in supplements.
It’s relatively cheap, and absorbs better than most other types.
Not all calcium carbonate is vegan, but most is.
Where Calcium Carbonate Comes From
It’s possible that calcium carbonate can come from oysters and mussel shells. That’s the only potential non-vegan source of it.
The problem is that I’ve never seen a supplement label the source of their calcium carbonate, but you could contact the manufacturer to be sure.
What I can say is that most calcium carbonate comes from limestone and other rocks.
It makes sense too. It’s going to be more efficient and cheaper for companies to extract it from rocks.
Is It Safe to Assume That Your Calcium Carbonate is Vegan?
With all that said, I think you can safely assume that almost all calcium carbonate is going to be vegan, particularly in supplements.
However, contact the product manufacturer to be sure.
Alternatively, you can choose a calcium supplement that is derived from algae. Many of the top vegan calcium supplements use it as a source.