gypsum - hand/display specimen of sugary white rock gypsum
Chemical formula: CaSO4・2H2O
Gypsum is primarily formed as a chemical precipitation in an evaporite environment. Gypsum and anhydrite are the most common sulfate minerals. This rock gypsum was deposited in a Permian age evaporite sequence over 100 feet thick interbedded with limestones of the Toroweap and Kaibab Formations. Both gypsum and anhydrite were mined at Weiser Ridge in Clark County, Nevada for use in the manufacture of gypsum wallboard. The quarry is now inactive.
Gypsum is a hydrated calcium sulfate - with two water molecules attached to the calcium sulfate. If it loses water it becomes anhydrite. If a bed of anhydrite picks up water, it swells, pushing up the sediments that lie above it to form a dome.
Gypsum is distinguishable from anhydrite by its lower Mohs hardness, 2.0 versus 3.5. They often look similar. Gypsum can be scratched by a fingernail where anhydrite can not. This gypsum is fairly typical, somewhat sugary in appearance, and passes the fingernail scratch test. You have to exert some pressure, using the edge of your thumbnail.
Select a specimen: When more than one specimen is shown, you can select a particular specimen by telling us what is in the photo with it, a black and silver pen, a black mechanical pencil, a blue and silver pen, or one of those plus some number of coins, or you can let us make the selection.
Ships in a Regional Priority Mail box. There would be room in that box for other specimens at no increase in postage. Please request an invoice to avoid overpaying shipping, by clicking the "combine shipping" button in the cart. Click > here < for shipping rates. Use back button to return to this page.
Making multiple purchases? Click on the "combine shipping" button in the shopping cart. We'll send an invoice with combined shipping. A link in that invoice will bring you back to checkout, no hassle.