What is a foraminifera shell made of?

Foraminifera shells, also known as tests, are primarily made of calcium carbonate (CaCO3), which can crystallize in different forms, such as calcite or aragonite. Some foraminifera, particularly those living in more extreme environments, may have shells composed of silica or organic material. The structure of these shells can vary greatly in shape and size, depending on the species. These shells are important in paleoceanography and geology, as they can provide insights into past environmental conditions.