Anhydrite

Anhydrite is a fascinating mineral made of calcium sulfate (CaSO₄), often found in layers of sedimentary rocks formed when ancient seas or salty lakes evaporated.

It’s typically white, gray, or pale blue, with a shiny, almost glassy look that catches the light. What makes anhydrite special is its dry nature—it doesn’t contain water in its structure, which sets it apart from its close cousin, gypsum.

Want to see a cool transformation? You can actually turn anhydrite into gypsum in a simple science experiment! Here’s how:

1.  Place a piece of anhydrite in a container.
2.  Slowly add water and let it soak.
3.  Over time, the anhydrite will absorb the water as it changes into gypsum (CaSO₄·2H₂O).

4. To reverse the process, simply let the gypsum dry completely.

This process adds two water molecules to its structure, resulting in volume expansion and a softer mineral. Naturally, this process can happen in environments with high moisture or groundwater, forming gypsum layers in sedimentary deposits.

You will receive a 1-2" specimen similar to those shown in photos.