How many calcium sulfate hemihydrates are there?

Calcium sulfate hemihydrate is one of the most consumed construction materials. In spite of its widespread use, its crystal structure remains a matter of debate. Two different types of hemihydrate, α and β, are known. Their different reactivity has until now been related to their different microstructure, with the α- being more reactive (i.e., providing a faster setting). Recent research conducted at the ESRF has introduced the possibility that a single crystal may contain multiple structural domains. Here, we intend to analyze calcium sulfate hemihydrate samples from diverse sources, including industrial and commercial samples with known high reactivity. Our goal is to establish connections between crystal structure and reactivity, investigating whether variations are attributable to microstructural features like surface area or differences in atomic structure. The results from this experiment will be of high value for the development of materials with tunable reactivity.