Mineral Species: Selenite after Glauberite

Chemical Formula: Na2SO4 and CaSO4-2(H2O)

Chemical Name: Sodium Sulphate and Calcium Sulphate

Mineral Class: Sulphate

Mineral Notes: Glauberite is a mineral known better for when it is not there. The reason is that Glauberite is highly soluble and is often replaced by other minerals such as Selenite, Calcite and Quartz. The replacement minerals often take on the shape of the original Glauberite even though their internal crystal structure is very different. Unlike these solid psedomorphs Glauberite can also form casts of itself. The original crystal becomes coated by another mineral after which its dissolves leaving an empty hollow as the only evidence of its past presence. Crystals of Glauberite are distinctive and difficult to describe. They are steeply inclined wedge to tabular shaped dipyramidal crystals. Glauberite forms in saline environments with other evaporite minerals.  

Description: This is an interesting specimen of Selenite which has completely replaced a crystal of Glauberite. The evidence of its previous existence is given by the highly distinctive shape, chracterised by very sharp face angles and terminations. A really good specimen of an interesting mineralogical curiosity.

Location: Camp Verde, Arizona, USA.