Crystal Clear Selenite

The Story
This is a very unusual, natural form of the mineral gypsum. When it appears in pure form like this it is known as selenite. Across the world, gypsum is a common mineral in oceanic and saline waters. When the environments are isolated concentrations of gypsum can become so high that they super-saturate the waters so that when the water dries up, crystals form. In most cases, the resulting gypsum crystals are clouded and colored by impurities. White Sands National Monument is an example of massive gypsum occurrence. All the sands there are composed of gypsum which formed on the floor of an inland sea eons ago. As the water and sediments dried up, the gypsum accumulated in massive quantities.

How They Formed
These particular selenite crystals are unique in their size and extreme clarity. Pure, water-clear crystals like this form only in certain geologic environments. In this case the story begins with a segment of inland sea that covered the area that is now southern Utah and northern Arizona during the Triassic Period about 240 million years ago. The waters here were quiet, allowing a thick accumulation of muds and clays. Eventually the area uplifted, the water receded, and the layers dried out. The gypsum concentrated and crystals grew as the layers were drying. If the process is prolonged, as in certain places such as our site in Arizona, the crystals can become very large. Pure gypsum is softer than your fingernail and scratches easily, so care must be taken in handling it. The crystals have perfect cleavage and can be split again and again into very fine sheets.