That's correct! Chalk is indeed a type of limestone formed from the fossilized remains of tiny marine organisms, mainly coccolithophores (a type of algae) and foraminifera (single-celled animals).

Here's a breakdown:

* Coccolithophores: These microscopic algae have hard, calcium carbonate plates called coccoliths that surround their cells. When they die, these coccoliths settle to the ocean floor.

* Foraminifera: These single-celled animals also have calcium carbonate shells. Their shells accumulate along with the coccoliths.

* Over time: The accumulation of these tiny fossils, along with other calcium carbonate material, forms thick layers on the ocean floor.

* Lithification: Through pressure and chemical reactions, these layers are cemented together, forming chalk.

So, the next time you see a piece of chalk, remember that you are holding billions of tiny fossils in your hand!