anhydrite
noun
an·hy·drite (ˌ)an-ˈhī-ˌdrīt 
: a mineral consisting of an anhydrous calcium sulfate that is usually massive and white or slightly colored
Example Sentences
Recent Examples on the Web Below 136 degrees Fahrenheit, gypsum is the more stable compound, and anhydrite will effortlessly dissolve in water, creating the building blocks for gypsum. 
Robin George Andrews, National Geographic, 22 Oct. 2019 Gypsum’s crystal makeup can accommodate a lot of water, producing plenty of volume using a relatively small mass of anhydrite. Robin George Andrews, National Geographic, 22 Oct. 2019
Robin George Andrews, National Geographic, 22 Oct. 2019 Gypsum’s crystal makeup can accommodate a lot of water, producing plenty of volume using a relatively small mass of anhydrite. Robin George Andrews, National Geographic, 22 Oct. 2019 Word History
Etymology
German Anhydrit, from Greek anydros
First Known Use
1805, in the meaning defined above