Is chalk made of diatoms

No, chalk is not made of diatoms. Chalk is primarily composed of calcite, a mineral form of calcium carbonate, which originates from the skeletal remains of marine organisms like coccolithophores and foraminifera. Diatoms, on the other hand, are a type of algae with silica-based cell walls, and they contribute to different types of sedimentary rocks. While both chalk and diatomaceous earth are formed from the remains of microscopic organisms, their compositions and origins differ significantly.