Gypsum in the form of colorless clear crystals.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "selenite" in a sentence
"There is a mineral called selenite which is also named after the word selene; however, selenite does not contain selenium."
"With this view, I will take a representative crystal, one easily dealt with, because it cleaves with great facility -- the crystal gypsum, or selenite, which is crystallized sulphate of lime."
"Ten years later, super-large sword-shaped crystals of selenite were found in a cavern at a depth of 120 meters."