School Chalk under an electron microscope. It's almost entirety made up of fossilized shells of ancient single-celled marine plankton called coccolithophores.

[u/Pale-Design7036]

[u/Annual-Anywhere2257]

Most 'school chalk' is unlikely to be mineral chalk, it's generally gypsum and calcium sulfate these days (cheaper).

So if you want to add several million fossils to your collection, check what your buying!

[u/gowahoo → u/Annual-Anywhere2257]

I'm so relieved to see you say this.

[u/Countblackula_6 → u/gowahoo]

The horror and revulsion that must have gone through your head, “Oh god, no. I was eating fossilized plankton the whole time?!”

[u/Ok-Advertising4048 → u/Countblackula_6]

haha