Desert lily

The “desert lily” is a (rarer) variety of gypsum crystallisation, like the famous “desert rose”, whose crystals incorporate grains of sand. A typical sedimentary mineral of chemical origin: it forms in evaporitic environments by direct precipitation from water or by hydration of anhydrite. The tabular, elongated crystals can reach up to a metre in length, and are often twinned in “swallowtail” or “spearhead” forms. Gypsum is a soft mineral (2 on the Mohs scale), light and easily cleaved into sheets and flakes. It is sometimes luminescent under ultraviolet rays.

Soluble in hydrochloric acid and also in hot water.