The Curio Cabinet series (#curioTuesday) is published biweekly, featuring an artifact of natural or cultural history and a brief selection of nifty facts. Curio Cabinet celebrates the history of curio collections, the roots of which played a part in the globalization of learning and scientific knowledge. Learn more here.

Today’s curio: selenite
Type: mineral
Origin: specimen unknown, but mineral is found worldwide
Size: about 3.5 inches tall x 1.5 inches wide at base

Selenite is a type of Gypsum, which is a sedimentary rock that formed as sea water evaporated out of prehistoric basins. Selenite is named for the Greek word for “moon,” (just as Selene was a Greek goddess of the moon) owing to its translucent or whitish hue. It forms tabular (flat plane), reticulated (forming net-like growths), or columnar crystals, as seen in the photo. It can also be transparent, or a translucent bluish hue, unless there are other minerals (or even fossils!) encapsulated inside. Gypsum has a hardness of 2 on the Mohs Scale, which means it’s pretty soft and can often be scratched with a fingernail.

The Basilica of Saint Sabina in Rome, Italy, is an ancient church that was built in the fifth century near a temple of the Roman and Greek goddess Juno (also known as Hera). Instead of using glass, its builders fashioned the church’s windows out of selenite, which permitted more light than typical early churches (with the reasoning that darker churches encouraged more introspection). This is the only account I could find of selenite being used for windows, but gypsum itself is an extremely common building material. The ancient Egyptians used rock gypsum for small vessels and figurines, while we still use it today for drywall when building houses.