What is Gypsum?
Gypsum is a soft hydrated calcium sulfate known for transparent selenite, fibrous satin spar and desert-rose forms.
Mineralogy and structure
The reference formula is CaSO4·2H2O. Gypsum is classified with the sulfates and its crystal system is monoclinic. Natural specimens can vary in composition, habit and degree of crystallinity, so the locality and observed form remain important.
Colour and appearance
Typical colours include colourless, white, grey, honey-yellow and brown. Lustre, transparency, inclusions and surface condition should be described for the individual specimen rather than inferred from the name alone.
Formation and localities
Gypsum forms in or is associated with evaporite basins, sedimentary beds, caves and hydrothermal settings. Notable collecting regions include Mexico, Morocco, Spain, Italy, the United States and Russia. A precise locality is more useful than a broad country label when it is documented.
Collecting notes
Gypsum is useful in a reference collection because its appearance connects mineral chemistry with geological setting. Store specimens dry, protected from impact and clearly labelled with the confirmed material, locality and any treatment history.
